物理化学学报2022，Vol.38Issue(4)：57-64,8.DOI:10.3866/PKU.WHXB202003046
不同结构导向剂合成不同硅含量SAPO-34分子筛的酸性质
Acid Properties of SAPO-34 Molecular Sieves with Different Si Contents Templated by Various Organic Structure-Directing Agents
摘要
Abstract
The acid properties of SAPO-34 molecular sieves(MSs),including the strength and density of Br?nsted acids,have attracted enormous attention in past decades because of the excellent performance of SAPO-34 in industrial processes such as the methanol-to-olefins(MTO)process and the selective catalytic reduction of NOx with NH3(NH3-SCR).Currently,pure-phase SAPO-34 MSs with different Si contents can be easily obtained by utilizing multifarious organic structure-directing agents(OSDAs).However,the resulting SAPO-34 MSs have different acid properties,which may affect their catalytic performance.Hence,correlating the acid properties with the OSDAs and Si contents is of significance to synthesize SAPO-34 MSs with the desired properties.Herein,the acid properties of four series of SAPO-34 MSs with varying Si contents synthesized using tetraethylammonium hydroxide(TEAOH),diisopropylamine(DIPA),n-butylamine(nBA),and morpholine(MOR)as the OSDAs were probed in detail by thermogravimetry(TG),Rietveld refinement,and solid-state nuclear magnetic resonance(ss-NMR)analyses.The strength and acid density were systematically investigated by exploring the host-guest interactions between the probed molecule CD3CN and the framework using 1H magic angle spinning(MAS)NMR spectroscopy,and the local environments of Si were studied by 29Si MAS NMR spectroscopy.The results of TG and Rietveld refinement showed that the SAPO-34 MSs templated by TEAOH and DIPA have only one OSDA per cha(one of the composite building units)cage in the longitudinal configuration,while those templated by nBA and MOR possess two OSDAs occluded in the cha cage in an up-and-down arrangement.Interestingly,the acid strength of SAPO-34 templated by TEAOH increased with increasing Si content,while the acid density remained almost unchanged.In contrast,the acid density of SAPO-34 templated by DIPA decreased evidently with an increase in the Si content,while the acid strength showed only a small variation.Among the other two samples,SAPO-34 templated by MOR has the most amounts of acid densities compared to SAPO-34 templated by nBA,while the strength is not superior.Thus,we conclude that the acid density is associated with the number of OSDAs in each cha cage and their protonation ability,while the difference in acid strength is attributed to the number of Si atoms at the edges of the Si islands.The findings of this study will provide insight into the acid properties of related crystalline porous materials.关键词
SAPO-34/有机模板剂/酸性质/固体核磁/结构精修/硅分布/多孔材料Key words
SAPO-34/OSDA/Acid property/ss-NMR/Rietveld refinement/Si distribution/Porous materials分类
化学化工引用本文复制引用
王磊,孙毯毯,闫娜娜,刘晓娜,马超,徐舒涛,郭鹏,田鹏,刘中民..不同结构导向剂合成不同硅含量SAPO-34分子筛的酸性质[J].物理化学学报,2022,38(4):57-64,8.基金项目
The project was supported by the National Natural Science Foundation of China(21972136,21676262,21991091),the CAS Pioneer Hundred Talents Program(Y706071202),the Dalian National Laboratory for Clean Energy,(DNL)Cooperation Fund,Chinese Academy of Sciences(DNL201908)and the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(QYZDBSSW-JSC040).国家自然科学基金(21972136,21676262,21991091),中国科学院百人计划(Y706071202),中国科学院洁净能源创新研究院合作基金(DNL201908)及中国科学院前沿科学重点研究计划(QYZDBSSW-JSC040)资助项目 （21972136,21676262,21991091）
