The cubic pyrochlore Dy2Pt2O7 was synthesized under 4 GPa and 1000℃ and its magnetic and thermodynamic properties were characterized by DC and AC magnetic susceptibility and specific heat down to 0.1 K.We found that ...The cubic pyrochlore Dy2Pt2O7 was synthesized under 4 GPa and 1000℃ and its magnetic and thermodynamic properties were characterized by DC and AC magnetic susceptibility and specific heat down to 0.1 K.We found that Dy2Pt2O7 does not form long-range magnetic order,but displays characteristics of canonical spin ice such as Dy2Pt2O7,including(1)a large effective moment 9.64μB close to the theoretical value and a small positive Curie-Weiss temperatureθCW=+0.77 K signaling a dominant ferromagnetic interaction among the Ising spins;(2)a saturation moment ~4.5μB being half of the total moment due to the local<111>Ising anisotropy;(3)thermally activated spin relaxation behaviors in the low(~1 K)and high(~20 K)temperature regions with different energy barriers and characteristic relaxation time;and most importantly,(4)the presence of a residual entropy close to Pauling’s estimation for water ice.展开更多
催化氧化技术是治理挥发性有机物(VOCs)的有效手段,其中新型催化剂的设计与优化是实现VOCs高效转化的关键。分别采用焙烧法与沉淀法制备了CeO_(2)活性载体,随后通过硼氢化钠还原法将Pt负载于CeO_(2)表面制备了Pt/CeO_(2)催化剂,进而考...催化氧化技术是治理挥发性有机物(VOCs)的有效手段,其中新型催化剂的设计与优化是实现VOCs高效转化的关键。分别采用焙烧法与沉淀法制备了CeO_(2)活性载体,随后通过硼氢化钠还原法将Pt负载于CeO_(2)表面制备了Pt/CeO_(2)催化剂,进而考察了不同制备方法对其催化氧化甲苯性能的影响。通过XRD、N_(2)吸/脱附、紫外拉曼光谱、XPS及O_(2)-TPD等手段对催化剂进行了表征。通过in situ DRIFTS研究了甲苯在反应过程中的演变行为。结果表明,不同制备方法均调控了Pt/CeO_(2)催化剂中活性氧物种的浓度。其中,沉淀-还原法制备的Pt/CeO_(2)-P催化剂具有更高的活性氧物种和氧空位浓度,促进了甲苯的活化与转化,使其生成易于降解的甲酸盐物种,并最终氧化为CO_(2)和H_(2)O。在甲苯浓度(体积分数)为0.1%、空速为48000 m L/(g·h)条件下,Pt/CeO_(2)-P催化剂的T50和T90(甲苯转化率达到50%和90%时的反应温度)分别低至157℃和168℃。展开更多
Supported metal catalysts are the backbone of heterogeneous catalysis,playing a crucial role in the modern chemical industry.Metal-support interactions(MSIs)are known important in determining the catalytic performance...Supported metal catalysts are the backbone of heterogeneous catalysis,playing a crucial role in the modern chemical industry.Metal-support interactions(MSIs)are known important in determining the catalytic performance of supported metal catalysts.This is particularly true for single-atom catalysts(SACs)and pseudo-single-atom catalysts(pseudo-SACs),where all metal atoms are dispersed on,and interact directly with the support.Consequently,the MSI of SACs and pseudo-SACs are theoretically more sensitive to modulation compared to that of traditional nanoparticle catalysts.In this work,we experimentally demonstrated this hypothesis by an observed size-dependent MSI modulation.We fabricated CoFe_(2)O_(4) supported Pt pseudo-SACs and nanoparticle catalysts,followed by a straightforward water treatment process.It was found that the covalent strong metal-support interaction(CMSI)in pseudo-SACs can be weakened,leading to a significant activity improvement in methane combustion reaction.This finding aligns with our recent observation of CoFe_(2)O_(4) supported Pt SACs.By contrast,the MSI in Pt nanoparticle catalyst was barely affected by the water treatment,giving rise to almost unchanged catalytic performance.This work highlights the critical role of metal size in determining the MSI modulation,offering a novel strategy for tuning the catalytic performance of SACs and pseudo-SACs by fine-tuning their MSIs.展开更多
基金Project supported by the National Key R&D Program of China(Grant No.2018YFA0305700)the National Natural Science Foundation of China(Grant Nos.11834016,11874400,and 11921004)+4 种基金the Beijing Natural Science Foundation,China(Grant No.Z190008)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.QYZDB-SSW-SLH013)the CAS Interdisciplinary Innovation Teamsupport of Grant No.NSF-DMR-1350002support of NSF DMR Grant No.1729588。
文摘The cubic pyrochlore Dy2Pt2O7 was synthesized under 4 GPa and 1000℃ and its magnetic and thermodynamic properties were characterized by DC and AC magnetic susceptibility and specific heat down to 0.1 K.We found that Dy2Pt2O7 does not form long-range magnetic order,but displays characteristics of canonical spin ice such as Dy2Pt2O7,including(1)a large effective moment 9.64μB close to the theoretical value and a small positive Curie-Weiss temperatureθCW=+0.77 K signaling a dominant ferromagnetic interaction among the Ising spins;(2)a saturation moment ~4.5μB being half of the total moment due to the local<111>Ising anisotropy;(3)thermally activated spin relaxation behaviors in the low(~1 K)and high(~20 K)temperature regions with different energy barriers and characteristic relaxation time;and most importantly,(4)the presence of a residual entropy close to Pauling’s estimation for water ice.
文摘催化氧化技术是治理挥发性有机物(VOCs)的有效手段,其中新型催化剂的设计与优化是实现VOCs高效转化的关键。分别采用焙烧法与沉淀法制备了CeO_(2)活性载体,随后通过硼氢化钠还原法将Pt负载于CeO_(2)表面制备了Pt/CeO_(2)催化剂,进而考察了不同制备方法对其催化氧化甲苯性能的影响。通过XRD、N_(2)吸/脱附、紫外拉曼光谱、XPS及O_(2)-TPD等手段对催化剂进行了表征。通过in situ DRIFTS研究了甲苯在反应过程中的演变行为。结果表明,不同制备方法均调控了Pt/CeO_(2)催化剂中活性氧物种的浓度。其中,沉淀-还原法制备的Pt/CeO_(2)-P催化剂具有更高的活性氧物种和氧空位浓度,促进了甲苯的活化与转化,使其生成易于降解的甲酸盐物种,并最终氧化为CO_(2)和H_(2)O。在甲苯浓度(体积分数)为0.1%、空速为48000 m L/(g·h)条件下,Pt/CeO_(2)-P催化剂的T50和T90(甲苯转化率达到50%和90%时的反应温度)分别低至157℃和168℃。
文摘Supported metal catalysts are the backbone of heterogeneous catalysis,playing a crucial role in the modern chemical industry.Metal-support interactions(MSIs)are known important in determining the catalytic performance of supported metal catalysts.This is particularly true for single-atom catalysts(SACs)and pseudo-single-atom catalysts(pseudo-SACs),where all metal atoms are dispersed on,and interact directly with the support.Consequently,the MSI of SACs and pseudo-SACs are theoretically more sensitive to modulation compared to that of traditional nanoparticle catalysts.In this work,we experimentally demonstrated this hypothesis by an observed size-dependent MSI modulation.We fabricated CoFe_(2)O_(4) supported Pt pseudo-SACs and nanoparticle catalysts,followed by a straightforward water treatment process.It was found that the covalent strong metal-support interaction(CMSI)in pseudo-SACs can be weakened,leading to a significant activity improvement in methane combustion reaction.This finding aligns with our recent observation of CoFe_(2)O_(4) supported Pt SACs.By contrast,the MSI in Pt nanoparticle catalyst was barely affected by the water treatment,giving rise to almost unchanged catalytic performance.This work highlights the critical role of metal size in determining the MSI modulation,offering a novel strategy for tuning the catalytic performance of SACs and pseudo-SACs by fine-tuning their MSIs.
