微波固相法制备ZnCl2/MCM-41催化剂及其催化性能

采用微波固相法、普通加热法和溶剂分散法等不同方法制备了ZnCl2/MCM-41催化剂,以XRD、FT-IR和TG-DSC等表征手段,比较了不同方法制备的催化剂中ZnCl2在分子筛表面的存在状态.XRD测定结果表明,微波固相法和溶剂分散法制备的样品可使ZnCl2完全分散于MCM-41分子筛表面,而加热法制备的样品中仍存在ZnCl2的晶相衍射峰.FT-IR、DSC和原子吸收光谱的测定结果表明,微波辐射可使ZnCl2与分子筛表面羟基发生固态相互作用形成O－Zn－Cl活性位,具有更加温和的Lewis酸性.考察了不同方法制备和不同ZnCl2负载量的催化剂在月桂烯与丙烯醛Diels-Alder反应中的催化性能,与普通加热法制备的催化剂相比,微波固相法与溶剂分散法制备的催化剂具有更好的催化活性和选择性,但微波固相法制备催化剂更为简单.

ZnCl2/MCM-41 Catalysts by the Solid-state Interaction under Microwave Heating and Their Catalytic Performances

ZnCl2/MCM-41 catalysts are prepared by solid-state interaction of ZnCl2 and mesoporous MCM-41 material using different method of microwave heating and conventional heating, as well as the method of solvent dispersion in toluene. The status of ZnCl2 onto the surface of MCM-41 in the samples of ZnCl2/MCM-41 is characterized by XRD, FT-IR, TG-DSC and atomic absorption spectroscopy (AAS).XRD patterns indicate that ZnCl2 can be dispersed completely on the surface of MCM-41 at ZnCl2 loading less than 4 mmol•g－1 if the samples prepared by the method of microwave heating and solvent dispersion. FT-IR spectra, DSC curves and AAS measurement results indicate that the new Lewis acid sites of O－Zn－Cl are formed by the solid-state interaction between ZnCl2 and the surface hydroxyl (Si－OH) under microwave heating. The catalytic performances of ZnCl2/MCM-41 samples prepared by the different methods are also investigated in the Diels-Alder reaction of myrcene and acrolein for high regioselective synthesis of para-myrac aldehyde. It was found that the activity, selectivity for cycloadducts and regiooselectivity of para-myrac aldehyde are higher over the catalysts of ZnCl2/MCM-41 prepared by the methods of microwave heating and solvent dispersion than that over ZnCl2/MCM-41 prepared by conventional heating. Apparently, the catalyst preparation method of microwave heating is simpler than the method of solvent dispersion in toluene. With an increase of ZnCl2 loading, the catalytic activity increases but the selectivity of cycloadducts decrease. The activity and regioselectivity of para/meta increase slightly with the selectivity for cycloadducts decrease markedly when ZnCl2 loading over 4 mmol•g－1,which suggested that new active sites of O－Zn－Cl formed on the surface of MCM-41 plays very important role for high regioselective synthesis of para-myrac aldehyde.