为了调控HZSM-5分子筛酸性,提升二甲苯异构化反应性能,对HZSM-5分子筛进行碱金属或碱土金属离子(M)交换制备不同nM/nAl(M=Li、Na、K、Rb、Cs、Mg、Ca、Sr、Ba)的HZSM-5分子筛样品,采用XRD、XRF、27Al MAS NMR、氮气物理吸附-脱附、吡啶...为了调控HZSM-5分子筛酸性,提升二甲苯异构化反应性能,对HZSM-5分子筛进行碱金属或碱土金属离子(M)交换制备不同nM/nAl(M=Li、Na、K、Rb、Cs、Mg、Ca、Sr、Ba)的HZSM-5分子筛样品,采用XRD、XRF、27Al MAS NMR、氮气物理吸附-脱附、吡啶吸附红外等手段对分子筛样品进行表征,并考察其催化二甲苯异构化反应性能。结果表明:碱金属及碱土金属离子交换不会明显影响HZSM-5分子筛孔道结构;随着制备过程初始配比n_(M)/n_(Al)从0.1逐渐增加至1.3,金属离子交换HZSM-5分子筛样品的n_(M)/n_(Al)逐渐升高,导致其Bronsted(B)酸酸量/Lewis(L)酸酸量比值(简称B/L酸量比)呈现降低趋势;同族金属中,金属离子交换HZSM-5分子筛样品的B/L酸量比降幅随原子序数的升高而增大,碱金属离子交换样品的B/L酸量比降幅较碱土金属离子交换样品更为显著。尽管HZSM-5分子筛样品中较低的B/L酸量比会降低乙苯转化率,但是有利于降低分子间歧化与烷基转移反应与分子内甲基顺位迁移反应比值,提高反应产物中对二甲苯/邻二甲苯摩尔比,可以获得更高的二甲苯收率和对二甲苯在二甲苯异构体中的占比。展开更多
MnO_(x)-CeO_(2)catalysts for the low-temperature selective catalytic reduction(SCR)of NO remain vulnerable to water and sulfur poisoning,limting their practical applications.Herein,we report a hydrophobic-modified MnO...MnO_(x)-CeO_(2)catalysts for the low-temperature selective catalytic reduction(SCR)of NO remain vulnerable to water and sulfur poisoning,limting their practical applications.Herein,we report a hydrophobic-modified MnO_(x)-CeO_(2)catalyst that achieves enhanced NO conversion rate and stability under harsh conditions.The catalyst was synthesized by decorating MnOx crystals with amorphous CeO_(2),followed by loading hydrophobic silica on the external surfaces.The hydrophobic silica allowed the adsorption of NH_(3)and NO and diffusion of H,suppressed the adsorption of H_(2)O,and prevented SO_(2)interaction with the Mn active sites,achieving selective molecular discrimination at the catalyst surface.At 120℃,under H_(2)O and SO_(2)exposure,the optimal hydrophobic catalyst maintains 82%NO conversion rate compared with 69%for the unmodified catalyst.The average adsorption energies of NH_(3),H_(2)O,and SO_(2)decreased by 0.05,0.43,and 0.52 eV,respectively.The NO reduction pathway follows the Eley-Rideal mechanism,NH_(3)^(*)+*→NH_(2)^(*)+H^(*)followed by NH_(2)^(*)+NO^(*)→N_(2)^(*)+H_(2)O^(*),with NH_(3)dehydrogenation being the rate determining step.Hydrophobic modification increased the activation energy for H atom transfer,leading to a minor decrease in the NO conversion rate at 120℃.This work demonstrates a viable strategy for developing robust NH_(3)-S CR catalysts capable of efficient operation in water-and sulfur-rich environments.展开更多
文摘为了调控HZSM-5分子筛酸性,提升二甲苯异构化反应性能,对HZSM-5分子筛进行碱金属或碱土金属离子(M)交换制备不同nM/nAl(M=Li、Na、K、Rb、Cs、Mg、Ca、Sr、Ba)的HZSM-5分子筛样品,采用XRD、XRF、27Al MAS NMR、氮气物理吸附-脱附、吡啶吸附红外等手段对分子筛样品进行表征,并考察其催化二甲苯异构化反应性能。结果表明:碱金属及碱土金属离子交换不会明显影响HZSM-5分子筛孔道结构;随着制备过程初始配比n_(M)/n_(Al)从0.1逐渐增加至1.3,金属离子交换HZSM-5分子筛样品的n_(M)/n_(Al)逐渐升高,导致其Bronsted(B)酸酸量/Lewis(L)酸酸量比值(简称B/L酸量比)呈现降低趋势;同族金属中,金属离子交换HZSM-5分子筛样品的B/L酸量比降幅随原子序数的升高而增大,碱金属离子交换样品的B/L酸量比降幅较碱土金属离子交换样品更为显著。尽管HZSM-5分子筛样品中较低的B/L酸量比会降低乙苯转化率,但是有利于降低分子间歧化与烷基转移反应与分子内甲基顺位迁移反应比值,提高反应产物中对二甲苯/邻二甲苯摩尔比,可以获得更高的二甲苯收率和对二甲苯在二甲苯异构体中的占比。
基金financially sponsored by the National Natural Science Foundation of China(No.52204414)the National Energy-Saving and Low-Carbon Materials Production and Application Demonstration Platform Program,China(No.TC220H06N)+1 种基金the National Key R&D Program of China(No.2021YFC1910504)the Fundamental Research Funds for the Central Universities,China(No.FRFTP-20-097A1Z)。
文摘MnO_(x)-CeO_(2)catalysts for the low-temperature selective catalytic reduction(SCR)of NO remain vulnerable to water and sulfur poisoning,limting their practical applications.Herein,we report a hydrophobic-modified MnO_(x)-CeO_(2)catalyst that achieves enhanced NO conversion rate and stability under harsh conditions.The catalyst was synthesized by decorating MnOx crystals with amorphous CeO_(2),followed by loading hydrophobic silica on the external surfaces.The hydrophobic silica allowed the adsorption of NH_(3)and NO and diffusion of H,suppressed the adsorption of H_(2)O,and prevented SO_(2)interaction with the Mn active sites,achieving selective molecular discrimination at the catalyst surface.At 120℃,under H_(2)O and SO_(2)exposure,the optimal hydrophobic catalyst maintains 82%NO conversion rate compared with 69%for the unmodified catalyst.The average adsorption energies of NH_(3),H_(2)O,and SO_(2)decreased by 0.05,0.43,and 0.52 eV,respectively.The NO reduction pathway follows the Eley-Rideal mechanism,NH_(3)^(*)+*→NH_(2)^(*)+H^(*)followed by NH_(2)^(*)+NO^(*)→N_(2)^(*)+H_(2)O^(*),with NH_(3)dehydrogenation being the rate determining step.Hydrophobic modification increased the activation energy for H atom transfer,leading to a minor decrease in the NO conversion rate at 120℃.This work demonstrates a viable strategy for developing robust NH_(3)-S CR catalysts capable of efficient operation in water-and sulfur-rich environments.
