Mesoporous activated carbons were prepared from direct coal liquefaction residue （CLR） by KOH activation method, and the experiments were carried out to investigate the effects of KOH/CLR ratio, solvent for mixing t...Mesoporous activated carbons were prepared from direct coal liquefaction residue （CLR） by KOH activation method, and the experiments were carried out to investigate the effects of KOH/CLR ratio, solvent for mixing the CLR and KOH, and carbonization procedure on the resultant carbon texture and catalytic activity for catalytic methane decomposition （CMD）. The results showed that optimal KOH/CLR ratio of 2 ： 1; solvent with higher solubility to KOH or the CLR, and an appropriate carbonization procedure are conductive to improving the carbon pore structure and catalytic activity for CMD. The resultant mesoporous carbons show higher and more stable activity than microporous carbons. Additionally, the relationship between the carbon textural properties and the catalytic activity for CMD was also discussed.展开更多
Different rare earth （RE=La, Ce, Pr, Nd, Sm, Y） and Cu modified nickel catalysts for hydrogen production from meth-ane decomposition were synthesized by a sol-gel process and method. The catalysts were characterized...Different rare earth （RE=La, Ce, Pr, Nd, Sm, Y） and Cu modified nickel catalysts for hydrogen production from meth-ane decomposition were synthesized by a sol-gel process and method. The catalysts were characterized or analyzed through Brumauer-Emmett-Teller （BET）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） techniques. And the hydrogen production performance was also evaluated by a fixed-bed and micro-reaction technique with CH4→C＋H2 as a probe reaction. The results showed that rare earth modification had played a great role for nickel catalysts, for example, smaller nickel particles, good thermal stability, high activity, etc. La was the best additive among rare earth modification. The SEM of rare earth modified catalysts showed ordered flower-like structure and rare earth modification made the nickel particles move to the surface of catalysts. In addition, the SEM of nano-carbons was also changed by rare earth modification with long, narrow nano-carbon fibers or tubes obtained. Solid carbon formation was prevented by rare earth modification.展开更多
Methane decomposition reaction has been studied at three different activation temperatures（500℃,800℃ and950℃）over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts.On co-impregnation of Ni...Methane decomposition reaction has been studied at three different activation temperatures（500℃,800℃ and950℃）over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts.On co-impregnation of Ni on Fe/Al2O3the activity of the catalyst was retained even at the high activation temperature at 950℃ and up to180 min.The Ni promotion enhanced the reducibility of Fe/Al2O3oxides showing higher catalytic activity with a hydrogen yield of 69%.The reactivity of bimetallic Mn and Fe over Al2O3catalyst decreased at 800℃ and 950℃ activation temperatures.Regeneration studies revealed that the catalyst could be effectively recycled up to 9times.The addition of O2（1 ml,2 ml,4 ml）in the feed enhanced substantially CH4conversion,the yield of hydrogen and the stability of the catalyst.展开更多
Effects of reaction temperature and methane gas hourly space velocity （GHSV） on methane decomposition over non-supported Ni catalyst have been investigated in this work.Methane molecules activation,Ni particles grow...Effects of reaction temperature and methane gas hourly space velocity （GHSV） on methane decomposition over non-supported Ni catalyst have been investigated in this work.Methane molecules activation,Ni particles growth and nano-carbon diffusion were the main factors influencing methane decomposition stability of non-supported Ni.The results of methane decomposition activity test on the non-supported Ni catalyst showed that the prepared non-supported Ni could exhibit a good methane decomposition performance with 273 gC/gNi and 2667 molH2/molNi at 500 -C and 45000 mL/（gcat h）.Scanning electron microscope （SEM）,X-ray powder diffraction （XRD） and temperature-programmed oxi- dation （TPO） have been carried out to characterize the used catalysts.The deposited carbon was carbon nanofibers,among which graphitic carbon formation increased with the reaction time of methane decomposition.Ni particle size was not the decisive factor during the carbon growing stage.展开更多
Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydroca...Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydrocarbon production. X-ray photoelectron spectroscopy （XPS）, static secondary ion mass spectrometry （SSIMS）, thermal gravimetric analysis （TGA）, Fourier transform infrared （FT-IR）, secondary electron microscopy/X-ray energy dispersive （SEM-EDX）, and temperature programmed desorption （TPD） were used to depict the chemistry of the catalytic results. These techniques revealed the changes in surface morphology and structure of Ni, Cu, Al, and K, and formation of bimetallic and trimetallic surface cationic sites with different cationic species, which resulted in the production of graphitic form of pure carbon on Ni：Cu/Al catalyst. The addition of K has a marked effect on the product selectivity and reactivity of the catalyst system. K addition restricts the formation of carbon on the surface and increases the production of hydrogen and C2, C3 hydrocarbons during the catalytic reaction whereas no hydrocarbons are produced on the sample without K. This study completely maps the modified surface structure and its relationship with the catalytic behavior of both systems. The process provides a flexible route for the production of carbon fibers and hydrogen on Ni：Cu/Al catalyst and hydrogen along with hydrocarbons on Ni：Cu：K/Al catalyst. The produced carbon fibers are imaged using a transmission electron microscope （TEM） for diameter size and wall structure determination. Hydrogen produced is COx free, which can be used directly in the fuel cell system. The effect of the addition of Cu and its transformation and interaction with Ni and K is responsible for the production of CO/CO2 free hydrogen, thus producing an environmental friendly clean energy.展开更多
The effects of additives containing iron or nickel during chemical vapor deposition(CVD)on the growth of carbon nanotubes(CNTs)by methane decomposition on Mo/MgO catalyst were investigated.Ferrocene and nickel nitrate...The effects of additives containing iron or nickel during chemical vapor deposition(CVD)on the growth of carbon nanotubes(CNTs)by methane decomposition on Mo/MgO catalyst were investigated.Ferrocene and nickel nitrate were introduced as deactivation inhibitors by in-situ evaporation during CVD.The precisely controlled in-situ introduction of these inhibitors increased the surface renewal of catalyst,and therefore prevented the catalyst from deactivation.Using this method,aligned multi-walled CNTs with parallel mesopores can be produced on a large scale.展开更多
Decomposition of methane in the presence of coprecipitated nickel-basedcatalysts to produce carbon fibers was investigated. The reaction was studied in the temperaturerange of 773 K to 1073 K. At 1023 K, the catalytic...Decomposition of methane in the presence of coprecipitated nickel-basedcatalysts to produce carbon fibers was investigated. The reaction was studied in the temperaturerange of 773 K to 1073 K. At 1023 K, the catalytic activities of three catalysts kept high at theinitial period and then decreased with the reaction time. The lifetimes of Ni-Cu-Al and Ni-La-Alcatalysts are longer than that of Ni-Al catalyst. With three catalysts, the yield of carbon fiberswas very low at 773 K. The yield of carbon fibers for Ni-La-Al catalyst was more than those forNi-Al and Ni-Cu-Al catalysts. For Ni-La-Al catalyst, the elevation of temperature from 873 K up to1073 K led gradually to an increase in the yield of carbon fibers. XRD studies on the Ni-La-Alcatalyst indicate that La_2NiO_4 was formed. The formation of La_2NiO_4 is responsible for theincrease in the catalytic lifetime and the yield of carbon fibers synthesized on Ni-La-Al at773-1073 K. Carbon fibers synthesized on Ni-Al catalyst are thin, long carbon nanotubes. There arebamboo-shaped carbon fibers synthesized on Ni-Cu-Al catalyst. Carbon fibers synthesized on Ni-La-Alcatalyst have large hollow core, thin wall and good graphitization.展开更多
Catalytic decomposition of methane,which produces high-purity hydrogen and high-value-added carbon nanomaterials,has shown considerable potential for development and is expected to yield significant economic benefits ...Catalytic decomposition of methane,which produces high-purity hydrogen and high-value-added carbon nanomaterials,has shown considerable potential for development and is expected to yield significant economic benefits in the future.However,designing catalysts that simultaneously exhibit high activity and long-term stability remains a significant challenge.Tuning the catalyst’s structure and electronic properties is an effective strategy for enhancing the reaction performance.In this work,a series of NixZr/ZSM-5 catalysts were prepared using the incipient wetness impregnation method,and the effect of Zr loadings on catalyst properties and performance was systematically investigated.The calcined and reduced catalysts were characterized by low-temperature N_(2)adsorption-desorption,XRD,SEM,H_(2)-TPR and XPS.The results showed that the addition of Zr significantly increased the specific surface area of the catalyst and reduced the metal particle size.Smaller NiO particles were found to enter the pores of the HZSM-5 support,and electronic interactions between NiO and ZrO_(2)markedly enhanced the metal-support interaction.The catalyst exhibited optimal catalytic performance at a Zr loading of 5%,achieving a maximum methane conversion of 68%at 625℃,maintaining activity for 900 min,and delivering a carbon yield of 1927%.Further increasing the Zr loading yielded only limited improvements in catalytic performance.Characterization of the spent catalysts and carbon products via TEM,Raman spectroscopy,and TGA revealed that the introduction of ZrO_(2)reduced metal sintering and promoted a shift in carbon nanofibers growth mode from tip-growth to base-growth.The mechanism of base-growth enabled the catalyst to maintain reaction activity for an extended period.展开更多
A comparative study of methane decomposition processes using NiFe catalyst,representing the transition metal group known for its ability to reduce activation energy,and graphite catalyst,representing carbon materials ...A comparative study of methane decomposition processes using NiFe catalyst,representing the transition metal group known for its ability to reduce activation energy,and graphite catalyst,representing carbon materials with diverse morphologies and abundant natural availability,was conducted using molecular dynamics simulations.The simulation findings suggest that a 100 K temperature increment results in only a very slight increase in the diffusion rate.The NiFe catalyst outperforms graphite in methane decomposition by providing both faster decomposition kinetics and significantly enhanced diffusion of carbon and hydrogen atoms.Nevertheless,the accumulation of these atomic species on the catalyst surface leads to the blockage of active sites and a decrease in catalytic activity.The activation energy required for the methane gas decomposition process with the NiFe catalyst is 0.20 eV,while with the graphite catalyst,it is 0.72 eV.In the methane gas decomposition process with NiFe catalyst,no CH,CH_(2),and CH_(3)bonds were found,indicating that methane decomposes directly and completely into hydrogen and carbon atoms separately.Meanwhile,with the graphite catalyst,the decomposition of CH_(4)into simpler compounds(CH,CH_(2),and CH_(3))was observed.展开更多
CO_(2)-free H_(2)refers to H_(2)production process without CO_(2)emission,which is a promising clean energy in the future.Catalytic decomposition of methane(CDM)is a competitive technology to produce CO_(2)-free H2 wi...CO_(2)-free H_(2)refers to H_(2)production process without CO_(2)emission,which is a promising clean energy in the future.Catalytic decomposition of methane(CDM)is a competitive technology to produce CO_(2)-free H2 with large-scale.However,CDM reaction is highly endothermic and is kinetically and thermodynamically unfavorable,which typically requires a harsh reaction temperature above 800℃.In this work,solar-driven photothermal catalytic decomposition of methane was firstly introduced to produce CO_(2)-free H_(2)relying solely on solar energy as the driving force.A high H_(2)yield of 204.6 mmol g^(–1)h^(–1)was observed over Ni-CeO2 interface under photothermal conditions,along with above 87%reduction in the apparent activation energy(11.2 vs.87.3 kJ mol^(–1))when comparing with the traditional thermal catalysis.Further studies suggested that Ni/CeO_(2)catalyst enhanced optical absorption in visible-infrared region to ensure the heat energy for methane decomposition.The generated electrons and holes participated in the redox process of photo-driven CDM reaction with enhanced separation ability of hot carriers excited by ultraviolet-visible light,which lowered activation energy and improved the photothermal catalytic activity.This work provides a promising photothermal catalytic strategy to produce CO_(2)-free H^(2)under mild conditions.展开更多
Catalysts Fe_(2)O_(3)-Al_(2)O_(3) with high Fe_(2)O_(3) contents(50-90wt%)were prepared by co-precipitation method and tested for methane decomposition and production of high-purity carbon nanofibers(CNFs).Catalytic t...Catalysts Fe_(2)O_(3)-Al_(2)O_(3) with high Fe_(2)O_(3) contents(50-90wt%)were prepared by co-precipitation method and tested for methane decomposition and production of high-purity carbon nanofibers(CNFs).Catalytic tests were conducted in a fixed-bed reactor at atmospheric pressure,different temperatures and high CH_(4) space velocities.The catalytic tests performed at 700℃ showed that Fe_(2)O_(3)-Al_(2)O_(3) catalysts containing 60-80wt% Fe_(2)O_(3) enable a maximal CH_(4) conversion of around 56%and production of CNFs with a purity above 95%.Further,the catalytic results recorded over 80%Fe_(2)O_(3)-Al_(2)O_(3) catalyst at varied temperatures and space velocities revealed the following:(1)increasing temperature leads to an increased maximum CH_(4) conversion but a reduced CNFs productivity per unit weight of catalyst,and(2)CNFs productivity can be maximized at each temperature by lowering CH_(4) space velocity to an appropriate rate through reducing CH_(4) feed rate or increasing the amount of catalyst fed in the reactor.Moreover,typical SEM,Raman and TEM characterization results confirmed that the CNFs obtained are of a relatively narrow diameter distribution of 20-40 nm and graphitic nanostructure in appearance.Furthermore,electroconductivity measurement of typical CNFs products confirmed their good electrical conductivity,suggesting their potential direct use for formulation of anti-static CNFs reinforced plastic composites.展开更多
The sustainability of methane catalytic decomposition is significantly enhanced by the production of high-quality value-added carbon products such as carbon nanotubes(CNTs).Understanding the production yields and prop...The sustainability of methane catalytic decomposition is significantly enhanced by the production of high-quality value-added carbon products such as carbon nanotubes(CNTs).Understanding the production yields and properties of CNTs is crucial for improving process feasibility and sustainability.This study employs machine learning technique to develop and analyze predictive models for the carbon yield and mean diameter of CNTs produced through methane catalytic decomposition.Utilizing comprehensive datasets from various experimental studies,the models incorporate variables related to catalyst composition,catalyst preparation,and operational parameters.Both models achieved high predictive accuracy,with R^(2)values exceeding 0.90.Notably,the reduction time during catalyst preparation was found to critically influence carbon yield,evidenced by a permutation importance value of 39.62%.Additionally,the use of Mo as a catalytic metal was observed to significantly reduce the diameter of produced CNTs.These findings highlight the need for future machine learning and simulation studies to include catalyst reduction parameters,thereby enhancing predictive accuracy and deepening process insights.This research provides strategic guidance for optimizing methane catalytic decomposition to produce enhanced CNTs,aligning with sustainability goals.展开更多
The increasing demands of hydrogen and the recent discovery of large reserves of methane have prompted the conversion of methane to hydrogen.The challenges raised by intensive CO_(2) emission from the traditional conv...The increasing demands of hydrogen and the recent discovery of large reserves of methane have prompted the conversion of methane to hydrogen.The challenges raised by intensive CO_(2) emission from the traditional conversion of methane have provoked emission-free hydrogen production from methane.The catalytic decomposition of methane(CDM) to produce hydrogen and advanced carbon hence comes into consideration due to the short process and environmental benignity.Although many researchers have made considerable progress in CDM research on the laboratory scale,CDM is still in its infancy in industrialization.The history of its development,fundamental mechanisms,and recent research progress in catalysts and catalytic systems are herein highlighted.The problems of catalytic interface degradation are reviewed,focusing on deactivation from coke deposition in the CDM process.The introduction of a liquid phase interface which can in-situ remove carbon products provides a new strategy for this process.Furthermore,the challenges and prospects for future research into novel CDM catalysts or catalyst systems are included.展开更多
Direct decomposition of methane was carried out using a fixed-bed reactor at 700 ℃ for the production of COx-free hydrogen and carbon nanofibers. The catalytic performance of NiO-M/SiO2 catalysts （where M=AgO, CoO, ...Direct decomposition of methane was carried out using a fixed-bed reactor at 700 ℃ for the production of COx-free hydrogen and carbon nanofibers. The catalytic performance of NiO-M/SiO2 catalysts （where M=AgO, CoO, CuO, FeO, MnOx and MoO） in methane decomposition was investigated. The experimental results indicate that among the tested catalysts, NiO/SiO2 promoted with CuO give the highest hydrogen yield. In addition, the examination of the most suitable catalyst support, including Al2O3, CeO2, La2O3, SiO2, and TiO2, shows that the decomposition of methane over NiO-CuO favors SiOx support. Furthermore, the optimum ratio of NiO to CuO on SiO2 support for methane decomposition was determined. The experimental results show that the optimum weight ratio of NiO to CuO fell at 8：2 （w/w） since the highest yield of hydrogen was obtained over this catalyst.展开更多
Bimetallic catalysts(Ni-Co/AC and Ni-Fe/AC)supported on activated carbon(AC)were prepared via one-step method from coal as AC precursor with the addition of metal salts by KOH activation.The effects of the introductio...Bimetallic catalysts(Ni-Co/AC and Ni-Fe/AC)supported on activated carbon(AC)were prepared via one-step method from coal as AC precursor with the addition of metal salts by KOH activation.The effects of the introduction of second metal(Co or Fe)into Ni/AC on the textural structure of the resultant bimetallic catalysts and their catalytic performances for methane decomposition were investigated.The results showed that active metals can be directly supported on AC by the reaction of metal species with carbon during the activation.The addition of Co or Fe to Ni/AC resulted in the decrease of specific surface area and pore volume.With increasing the loading of Co or Fe,metal alloys were formed and total surface area and pore volume declined,but the mesoporosity was increased.Bimetallic Ni-Co/AC and Ni-Fe/AC catalysts exhibited better catalytic activity and stability for methane decomposition compared than Ni/AC.The introduction of Co mainly improved initial catalytic activity;however,Ni-Fe/AC catalyst showed better behaviors in terms of reducing the deactivation rate of Ni-based catalyst than Ni-Co/AC catalyst,which is relative with the formation of Ni-Fe alloy and carbon fibers over Ni-Fe/AC.This work provides a simple and efficient approach to improve catalytic performances of Ni-based catalyst for methane decomposition.展开更多
Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel.Studies have been conducted on the different aspects of hydrogen,including it...Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel.Studies have been conducted on the different aspects of hydrogen,including its production,storage,transportation and utilization.The catalytic methane decomposition technique for hydrogen production is an environmentally friendly process that avoids generating carbon dioxide gas,which contributes to the greenhouse effect.Catalysts play a crucial role in facilitating rapid,cost-effective and efficient production of hydrogen using this technique.In this study,reactive molecular dynamics simulations were employed to examine the impact of Pt_(7) cluster decoration on the surface of a Ni(110)catalyst,referred to as Pt_(7)-Ni(110),on the rates of methane dissociation and molecular hydrogen production.The reactive force field was employed to model the atomic interactions that enabled the formation and dissociation of chemical bonds.Our reactive molecular dynamics simulations using the Pt_(7)-Ni(110)catalyst revealed a notable decrease in the number of methane molecules,specifically~11.89 molecules per picosecond.The rate was approximately four times higher than that of the simulation system utilizing a Ni(110)catalyst and approximately six times higher than that of the pure methane,no-catalyst system.The number of hydrogen molecules generated during a simulation period of 150000 fs was greater on the Pt_(7)-Ni(110)surface than in both the Ni(110)and pure methane systems.This was due to the presence of numerous dissociated hydrogen atoms on the Pt_(7)-Ni(110)surface.展开更多
This article reports the production of COx free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al2O3-SiO2 catalysts. The influence of reaction temperature, pretreatment temperature, a...This article reports the production of COx free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al2O3-SiO2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si （4 ： 0.5 ： 1.5） catalyst reduced with hydrazine hydrate produced better H2 yields of ca. 1815 mol H2/mol Ni than the catalyst reduced with 5% H2/N2.展开更多
The development of zeolites possessing dendritic features represents a great opportunity for the design of novel materials with applications in a large variety of fields and,in particular,in the energy sector to affor...The development of zeolites possessing dendritic features represents a great opportunity for the design of novel materials with applications in a large variety of fields and,in particular,in the energy sector to afford its transition towards a low carbon system.In the current work,ZSM-5 zeolite showing a dendritic3D nanoarchitecture has been synthesized by the functionalization of protozeolitic nanounits with an amphiphilic organosilane,which provokes the branched aggregative growth of zeolite embryos.Dendritic ZSM-5 exhibits outstanding accessibility arising from a highly interconnected network of radially-oriented mesopores(3-10 nm)and large cavities(20-80 nm),which add to the zeolitic micropores,thus showing a well-defined trimodal pore size distribution.These singular features provide dendritic ZSM-5 with sharply enhanced performance in comparison with nano-and hierarchical reference materials when tested in a number of energy related applications,such as VOCs(toluene)adsorption(improved capacity),plastics(low-density polyethylene)catalytic cracking(boosted activity)and hydrogen production by methane catalytic decomposition(higher activity and deactivation resistance).展开更多
The Co Mg O and Co Mn Mg O catalysts are prepared by a co-precipitation method and used as the catalysts for the synthesis of carbon nanotubes（CNTs） through the catalytic chemical vapor deposition（CCVD）. The effec...The Co Mg O and Co Mn Mg O catalysts are prepared by a co-precipitation method and used as the catalysts for the synthesis of carbon nanotubes（CNTs） through the catalytic chemical vapor deposition（CCVD）. The effects of Mn addition on the carbon yield and structure are investigated. The catalysts are characterized by temperature programmed reduction（TPR） and X-ray diffraction（XRD） techniques, and the synthesized carbon materials are characterized by transmission electron microscopy（TEM） and thermo gravimetric analysis（TG）. TEM measurement indicates that the catalyst Co Mg O enclosed completely in the produced graphite layer results in the deactivation of the catalyst. TG results suggest that the Co Mn Mg O catalyst has a higher selectivity for CNTs than Co Mg O. Meanwhile, different diameters of CNTs are synthesized by Co Mn Mg O catalysts with various amounts of Co content, and the results show that the addition of Mn avoids forming the enclosed catalyst, prevents the formation of amorphous carbon, subsequently promotes the growth of CNTs, and the catalyst with decreased Co content is favorable for the synthesis of CNTs with a narrow diameter distribution.The Co Mn Mg O catalyst with 40% Co content has superior catalytic activity for the growth of carbon nanotubes.展开更多
基金supported by the National Natural Science Foundation of China(No.20906009)the Key Program Project of Joint Fund of Coal Research by NSFC and Shenhua Group(No.51134014)+2 种基金the Fundamental Research Funds for the Central Universities(No.DUT12JN05)the National Basic Research Program of China(973Program)the Ministry of Science and Technology,China(No.2011CB201301)
文摘Mesoporous activated carbons were prepared from direct coal liquefaction residue （CLR） by KOH activation method, and the experiments were carried out to investigate the effects of KOH/CLR ratio, solvent for mixing the CLR and KOH, and carbonization procedure on the resultant carbon texture and catalytic activity for catalytic methane decomposition （CMD）. The results showed that optimal KOH/CLR ratio of 2 ： 1; solvent with higher solubility to KOH or the CLR, and an appropriate carbonization procedure are conductive to improving the carbon pore structure and catalytic activity for CMD. The resultant mesoporous carbons show higher and more stable activity than microporous carbons. Additionally, the relationship between the carbon textural properties and the catalytic activity for CMD was also discussed.
基金supported by the Twelfth Five-year National Science and Technology Pillar Program(2012BAE01B02)
文摘Different rare earth （RE=La, Ce, Pr, Nd, Sm, Y） and Cu modified nickel catalysts for hydrogen production from meth-ane decomposition were synthesized by a sol-gel process and method. The catalysts were characterized or analyzed through Brumauer-Emmett-Teller （BET）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） techniques. And the hydrogen production performance was also evaluated by a fixed-bed and micro-reaction technique with CH4→C＋H2 as a probe reaction. The results showed that rare earth modification had played a great role for nickel catalysts, for example, smaller nickel particles, good thermal stability, high activity, etc. La was the best additive among rare earth modification. The SEM of rare earth modified catalysts showed ordered flower-like structure and rare earth modification made the nickel particles move to the surface of catalysts. In addition, the SEM of nano-carbons was also changed by rare earth modification with long, narrow nano-carbon fibers or tubes obtained. Solid carbon formation was prevented by rare earth modification.
基金the Deanship of Scientific Research at King Saud University for its funding this research group No.(RG-1436-119)
文摘Methane decomposition reaction has been studied at three different activation temperatures（500℃,800℃ and950℃）over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts.On co-impregnation of Ni on Fe/Al2O3the activity of the catalyst was retained even at the high activation temperature at 950℃ and up to180 min.The Ni promotion enhanced the reducibility of Fe/Al2O3oxides showing higher catalytic activity with a hydrogen yield of 69%.The reactivity of bimetallic Mn and Fe over Al2O3catalyst decreased at 800℃ and 950℃ activation temperatures.Regeneration studies revealed that the catalyst could be effectively recycled up to 9times.The addition of O2（1 ml,2 ml,4 ml）in the feed enhanced substantially CH4conversion,the yield of hydrogen and the stability of the catalyst.
文摘Effects of reaction temperature and methane gas hourly space velocity （GHSV） on methane decomposition over non-supported Ni catalyst have been investigated in this work.Methane molecules activation,Ni particles growth and nano-carbon diffusion were the main factors influencing methane decomposition stability of non-supported Ni.The results of methane decomposition activity test on the non-supported Ni catalyst showed that the prepared non-supported Ni could exhibit a good methane decomposition performance with 273 gC/gNi and 2667 molH2/molNi at 500 -C and 45000 mL/（gcat h）.Scanning electron microscope （SEM）,X-ray powder diffraction （XRD） and temperature-programmed oxi- dation （TPO） have been carried out to characterize the used catalysts.The deposited carbon was carbon nanofibers,among which graphitic carbon formation increased with the reaction time of methane decomposition.Ni particle size was not the decisive factor during the carbon growing stage.
文摘Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydrocarbon production. X-ray photoelectron spectroscopy （XPS）, static secondary ion mass spectrometry （SSIMS）, thermal gravimetric analysis （TGA）, Fourier transform infrared （FT-IR）, secondary electron microscopy/X-ray energy dispersive （SEM-EDX）, and temperature programmed desorption （TPD） were used to depict the chemistry of the catalytic results. These techniques revealed the changes in surface morphology and structure of Ni, Cu, Al, and K, and formation of bimetallic and trimetallic surface cationic sites with different cationic species, which resulted in the production of graphitic form of pure carbon on Ni：Cu/Al catalyst. The addition of K has a marked effect on the product selectivity and reactivity of the catalyst system. K addition restricts the formation of carbon on the surface and increases the production of hydrogen and C2, C3 hydrocarbons during the catalytic reaction whereas no hydrocarbons are produced on the sample without K. This study completely maps the modified surface structure and its relationship with the catalytic behavior of both systems. The process provides a flexible route for the production of carbon fibers and hydrogen on Ni：Cu/Al catalyst and hydrogen along with hydrocarbons on Ni：Cu：K/Al catalyst. The produced carbon fibers are imaged using a transmission electron microscope （TEM） for diameter size and wall structure determination. Hydrogen produced is COx free, which can be used directly in the fuel cell system. The effect of the addition of Cu and its transformation and interaction with Ni and K is responsible for the production of CO/CO2 free hydrogen, thus producing an environmental friendly clean energy.
基金supported by the Guangdong Provincial Natural Science Foundation(No.31420)the Guangzhou City Science andTechnology Project(No.2003Z3-D2071)the Guangdong Provincial Science and Technology Project(No.2006 A10903002).
文摘The effects of additives containing iron or nickel during chemical vapor deposition(CVD)on the growth of carbon nanotubes(CNTs)by methane decomposition on Mo/MgO catalyst were investigated.Ferrocene and nickel nitrate were introduced as deactivation inhibitors by in-situ evaporation during CVD.The precisely controlled in-situ introduction of these inhibitors increased the surface renewal of catalyst,and therefore prevented the catalyst from deactivation.Using this method,aligned multi-walled CNTs with parallel mesopores can be produced on a large scale.
基金Supported by the National Natural Science Foundation of China (No. 20263003)Natural Science Foundation of Jiangxi province (No. 0250009)
文摘Decomposition of methane in the presence of coprecipitated nickel-basedcatalysts to produce carbon fibers was investigated. The reaction was studied in the temperaturerange of 773 K to 1073 K. At 1023 K, the catalytic activities of three catalysts kept high at theinitial period and then decreased with the reaction time. The lifetimes of Ni-Cu-Al and Ni-La-Alcatalysts are longer than that of Ni-Al catalyst. With three catalysts, the yield of carbon fiberswas very low at 773 K. The yield of carbon fibers for Ni-La-Al catalyst was more than those forNi-Al and Ni-Cu-Al catalysts. For Ni-La-Al catalyst, the elevation of temperature from 873 K up to1073 K led gradually to an increase in the yield of carbon fibers. XRD studies on the Ni-La-Alcatalyst indicate that La_2NiO_4 was formed. The formation of La_2NiO_4 is responsible for theincrease in the catalytic lifetime and the yield of carbon fibers synthesized on Ni-La-Al at773-1073 K. Carbon fibers synthesized on Ni-Al catalyst are thin, long carbon nanotubes. There arebamboo-shaped carbon fibers synthesized on Ni-Cu-Al catalyst. Carbon fibers synthesized on Ni-La-Alcatalyst have large hollow core, thin wall and good graphitization.
基金Supported by Innovative Research Groups of the National Natural Science Foundation of China(22021004)。
文摘Catalytic decomposition of methane,which produces high-purity hydrogen and high-value-added carbon nanomaterials,has shown considerable potential for development and is expected to yield significant economic benefits in the future.However,designing catalysts that simultaneously exhibit high activity and long-term stability remains a significant challenge.Tuning the catalyst’s structure and electronic properties is an effective strategy for enhancing the reaction performance.In this work,a series of NixZr/ZSM-5 catalysts were prepared using the incipient wetness impregnation method,and the effect of Zr loadings on catalyst properties and performance was systematically investigated.The calcined and reduced catalysts were characterized by low-temperature N_(2)adsorption-desorption,XRD,SEM,H_(2)-TPR and XPS.The results showed that the addition of Zr significantly increased the specific surface area of the catalyst and reduced the metal particle size.Smaller NiO particles were found to enter the pores of the HZSM-5 support,and electronic interactions between NiO and ZrO_(2)markedly enhanced the metal-support interaction.The catalyst exhibited optimal catalytic performance at a Zr loading of 5%,achieving a maximum methane conversion of 68%at 625℃,maintaining activity for 900 min,and delivering a carbon yield of 1927%.Further increasing the Zr loading yielded only limited improvements in catalytic performance.Characterization of the spent catalysts and carbon products via TEM,Raman spectroscopy,and TGA revealed that the introduction of ZrO_(2)reduced metal sintering and promoted a shift in carbon nanofibers growth mode from tip-growth to base-growth.The mechanism of base-growth enabled the catalyst to maintain reaction activity for an extended period.
基金the financial support provided by Universitas Brawijaya through research grant contract number 00140.2/UN10.A0501/B/PT.01.03.2/2024.
文摘A comparative study of methane decomposition processes using NiFe catalyst,representing the transition metal group known for its ability to reduce activation energy,and graphite catalyst,representing carbon materials with diverse morphologies and abundant natural availability,was conducted using molecular dynamics simulations.The simulation findings suggest that a 100 K temperature increment results in only a very slight increase in the diffusion rate.The NiFe catalyst outperforms graphite in methane decomposition by providing both faster decomposition kinetics and significantly enhanced diffusion of carbon and hydrogen atoms.Nevertheless,the accumulation of these atomic species on the catalyst surface leads to the blockage of active sites and a decrease in catalytic activity.The activation energy required for the methane gas decomposition process with the NiFe catalyst is 0.20 eV,while with the graphite catalyst,it is 0.72 eV.In the methane gas decomposition process with NiFe catalyst,no CH,CH_(2),and CH_(3)bonds were found,indicating that methane decomposes directly and completely into hydrogen and carbon atoms separately.Meanwhile,with the graphite catalyst,the decomposition of CH_(4)into simpler compounds(CH,CH_(2),and CH_(3))was observed.
文摘CO_(2)-free H_(2)refers to H_(2)production process without CO_(2)emission,which is a promising clean energy in the future.Catalytic decomposition of methane(CDM)is a competitive technology to produce CO_(2)-free H2 with large-scale.However,CDM reaction is highly endothermic and is kinetically and thermodynamically unfavorable,which typically requires a harsh reaction temperature above 800℃.In this work,solar-driven photothermal catalytic decomposition of methane was firstly introduced to produce CO_(2)-free H_(2)relying solely on solar energy as the driving force.A high H_(2)yield of 204.6 mmol g^(–1)h^(–1)was observed over Ni-CeO2 interface under photothermal conditions,along with above 87%reduction in the apparent activation energy(11.2 vs.87.3 kJ mol^(–1))when comparing with the traditional thermal catalysis.Further studies suggested that Ni/CeO_(2)catalyst enhanced optical absorption in visible-infrared region to ensure the heat energy for methane decomposition.The generated electrons and holes participated in the redox process of photo-driven CDM reaction with enhanced separation ability of hot carriers excited by ultraviolet-visible light,which lowered activation energy and improved the photothermal catalytic activity.This work provides a promising photothermal catalytic strategy to produce CO_(2)-free H^(2)under mild conditions.
基金supported by National Natural Science Foundation of China(U21A20316).
文摘Catalysts Fe_(2)O_(3)-Al_(2)O_(3) with high Fe_(2)O_(3) contents(50-90wt%)were prepared by co-precipitation method and tested for methane decomposition and production of high-purity carbon nanofibers(CNFs).Catalytic tests were conducted in a fixed-bed reactor at atmospheric pressure,different temperatures and high CH_(4) space velocities.The catalytic tests performed at 700℃ showed that Fe_(2)O_(3)-Al_(2)O_(3) catalysts containing 60-80wt% Fe_(2)O_(3) enable a maximal CH_(4) conversion of around 56%and production of CNFs with a purity above 95%.Further,the catalytic results recorded over 80%Fe_(2)O_(3)-Al_(2)O_(3) catalyst at varied temperatures and space velocities revealed the following:(1)increasing temperature leads to an increased maximum CH_(4) conversion but a reduced CNFs productivity per unit weight of catalyst,and(2)CNFs productivity can be maximized at each temperature by lowering CH_(4) space velocity to an appropriate rate through reducing CH_(4) feed rate or increasing the amount of catalyst fed in the reactor.Moreover,typical SEM,Raman and TEM characterization results confirmed that the CNFs obtained are of a relatively narrow diameter distribution of 20-40 nm and graphitic nanostructure in appearance.Furthermore,electroconductivity measurement of typical CNFs products confirmed their good electrical conductivity,suggesting their potential direct use for formulation of anti-static CNFs reinforced plastic composites.
基金supported by the Agency for Science,Technology and Research(A*STAR),Singapore,under the project Methane Pyrolysis for Hydrogen and Carbon Nanotube Production via Novel Catalytic Membrane Reactor System(No.U2102d2011)。
文摘The sustainability of methane catalytic decomposition is significantly enhanced by the production of high-quality value-added carbon products such as carbon nanotubes(CNTs).Understanding the production yields and properties of CNTs is crucial for improving process feasibility and sustainability.This study employs machine learning technique to develop and analyze predictive models for the carbon yield and mean diameter of CNTs produced through methane catalytic decomposition.Utilizing comprehensive datasets from various experimental studies,the models incorporate variables related to catalyst composition,catalyst preparation,and operational parameters.Both models achieved high predictive accuracy,with R^(2)values exceeding 0.90.Notably,the reduction time during catalyst preparation was found to critically influence carbon yield,evidenced by a permutation importance value of 39.62%.Additionally,the use of Mo as a catalytic metal was observed to significantly reduce the diameter of produced CNTs.These findings highlight the need for future machine learning and simulation studies to include catalyst reduction parameters,thereby enhancing predictive accuracy and deepening process insights.This research provides strategic guidance for optimizing methane catalytic decomposition to produce enhanced CNTs,aligning with sustainability goals.
基金the funding support from the National Natural Science Foundation of China(51722404,51674177,51804221 and 91845113)the National Key R&D Program of China(2018YFE0201703)+2 种基金the China Postdoctoral Science Foundation(2018M642906 and 2019T120684)the Fundamental Research Funds for the Central Universities(2042019kf0230)the Hubei Provincial Natural Science Foundation of China(2019CFA065)。
文摘The increasing demands of hydrogen and the recent discovery of large reserves of methane have prompted the conversion of methane to hydrogen.The challenges raised by intensive CO_(2) emission from the traditional conversion of methane have provoked emission-free hydrogen production from methane.The catalytic decomposition of methane(CDM) to produce hydrogen and advanced carbon hence comes into consideration due to the short process and environmental benignity.Although many researchers have made considerable progress in CDM research on the laboratory scale,CDM is still in its infancy in industrialization.The history of its development,fundamental mechanisms,and recent research progress in catalysts and catalytic systems are herein highlighted.The problems of catalytic interface degradation are reviewed,focusing on deactivation from coke deposition in the CDM process.The introduction of a liquid phase interface which can in-situ remove carbon products provides a new strategy for this process.Furthermore,the challenges and prospects for future research into novel CDM catalysts or catalyst systems are included.
文摘Direct decomposition of methane was carried out using a fixed-bed reactor at 700 ℃ for the production of COx-free hydrogen and carbon nanofibers. The catalytic performance of NiO-M/SiO2 catalysts （where M=AgO, CoO, CuO, FeO, MnOx and MoO） in methane decomposition was investigated. The experimental results indicate that among the tested catalysts, NiO/SiO2 promoted with CuO give the highest hydrogen yield. In addition, the examination of the most suitable catalyst support, including Al2O3, CeO2, La2O3, SiO2, and TiO2, shows that the decomposition of methane over NiO-CuO favors SiOx support. Furthermore, the optimum ratio of NiO to CuO on SiO2 support for methane decomposition was determined. The experimental results show that the optimum weight ratio of NiO to CuO fell at 8：2 （w/w） since the highest yield of hydrogen was obtained over this catalyst.
基金the National Natural Science Foundation of China(No.21878044,U1503194).
文摘Bimetallic catalysts(Ni-Co/AC and Ni-Fe/AC)supported on activated carbon(AC)were prepared via one-step method from coal as AC precursor with the addition of metal salts by KOH activation.The effects of the introduction of second metal(Co or Fe)into Ni/AC on the textural structure of the resultant bimetallic catalysts and their catalytic performances for methane decomposition were investigated.The results showed that active metals can be directly supported on AC by the reaction of metal species with carbon during the activation.The addition of Co or Fe to Ni/AC resulted in the decrease of specific surface area and pore volume.With increasing the loading of Co or Fe,metal alloys were formed and total surface area and pore volume declined,but the mesoporosity was increased.Bimetallic Ni-Co/AC and Ni-Fe/AC catalysts exhibited better catalytic activity and stability for methane decomposition compared than Ni/AC.The introduction of Co mainly improved initial catalytic activity;however,Ni-Fe/AC catalyst showed better behaviors in terms of reducing the deactivation rate of Ni-based catalyst than Ni-Co/AC catalyst,which is relative with the formation of Ni-Fe alloy and carbon fibers over Ni-Fe/AC.This work provides a simple and efficient approach to improve catalytic performances of Ni-based catalyst for methane decomposition.
基金funded by a PFR 2023 research grant from the Ministry of Education,Culture,Research,and Technology of the Republic of Indonesia(contract number 183/E5/PG/02.00.PL/2023).
文摘Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel.Studies have been conducted on the different aspects of hydrogen,including its production,storage,transportation and utilization.The catalytic methane decomposition technique for hydrogen production is an environmentally friendly process that avoids generating carbon dioxide gas,which contributes to the greenhouse effect.Catalysts play a crucial role in facilitating rapid,cost-effective and efficient production of hydrogen using this technique.In this study,reactive molecular dynamics simulations were employed to examine the impact of Pt_(7) cluster decoration on the surface of a Ni(110)catalyst,referred to as Pt_(7)-Ni(110),on the rates of methane dissociation and molecular hydrogen production.The reactive force field was employed to model the atomic interactions that enabled the formation and dissociation of chemical bonds.Our reactive molecular dynamics simulations using the Pt_(7)-Ni(110)catalyst revealed a notable decrease in the number of methane molecules,specifically~11.89 molecules per picosecond.The rate was approximately four times higher than that of the simulation system utilizing a Ni(110)catalyst and approximately six times higher than that of the pure methane,no-catalyst system.The number of hydrogen molecules generated during a simulation period of 150000 fs was greater on the Pt_(7)-Ni(110)surface than in both the Ni(110)and pure methane systems.This was due to the presence of numerous dissociated hydrogen atoms on the Pt_(7)-Ni(110)surface.
文摘This article reports the production of COx free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al2O3-SiO2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si （4 ： 0.5 ： 1.5） catalyst reduced with hydrazine hydrate produced better H2 yields of ca. 1815 mol H2/mol Ni than the catalyst reduced with 5% H2/N2.
基金the Max Planck society for its supportthe Ministry of Universities+3 种基金the Recovery,Transformation and Resilience Planthe Autonomous University of Madrid for a research grant(CA1/RSUE/2021-00836)supported by the Spanish Government‘‘Ministerio de Economía.Industriay Competitividad"(BIOCASCHEM CTQ2017-87001-R)European Research Council Horizon 2020 research an innovation program TODENZE project(ERC101021502)。
文摘The development of zeolites possessing dendritic features represents a great opportunity for the design of novel materials with applications in a large variety of fields and,in particular,in the energy sector to afford its transition towards a low carbon system.In the current work,ZSM-5 zeolite showing a dendritic3D nanoarchitecture has been synthesized by the functionalization of protozeolitic nanounits with an amphiphilic organosilane,which provokes the branched aggregative growth of zeolite embryos.Dendritic ZSM-5 exhibits outstanding accessibility arising from a highly interconnected network of radially-oriented mesopores(3-10 nm)and large cavities(20-80 nm),which add to the zeolitic micropores,thus showing a well-defined trimodal pore size distribution.These singular features provide dendritic ZSM-5 with sharply enhanced performance in comparison with nano-and hierarchical reference materials when tested in a number of energy related applications,such as VOCs(toluene)adsorption(improved capacity),plastics(low-density polyethylene)catalytic cracking(boosted activity)and hydrogen production by methane catalytic decomposition(higher activity and deactivation resistance).
基金Project supported by the National Basic Research Program of China(Grant No.2011CB201202)
文摘The Co Mg O and Co Mn Mg O catalysts are prepared by a co-precipitation method and used as the catalysts for the synthesis of carbon nanotubes（CNTs） through the catalytic chemical vapor deposition（CCVD）. The effects of Mn addition on the carbon yield and structure are investigated. The catalysts are characterized by temperature programmed reduction（TPR） and X-ray diffraction（XRD） techniques, and the synthesized carbon materials are characterized by transmission electron microscopy（TEM） and thermo gravimetric analysis（TG）. TEM measurement indicates that the catalyst Co Mg O enclosed completely in the produced graphite layer results in the deactivation of the catalyst. TG results suggest that the Co Mn Mg O catalyst has a higher selectivity for CNTs than Co Mg O. Meanwhile, different diameters of CNTs are synthesized by Co Mn Mg O catalysts with various amounts of Co content, and the results show that the addition of Mn avoids forming the enclosed catalyst, prevents the formation of amorphous carbon, subsequently promotes the growth of CNTs, and the catalyst with decreased Co content is favorable for the synthesis of CNTs with a narrow diameter distribution.The Co Mn Mg O catalyst with 40% Co content has superior catalytic activity for the growth of carbon nanotubes.
