Cs-Nb/SiO2酸碱双功能催化剂催化羟醛缩合制MMA性能研究OA

During aldol condensation to methyl methacrylate(MMA),the catalyst often has poor reaction stability due to carbon deposition.The strong acid and strong base sites on surface of the catalyst are important reasons for carbon deposition on catalyst,and the method of eliminating the strong acid and strong base sites on surface of the catalyst can be used to improve stability of the catalyst.A series of acid-base bifunctional catalysts were prepared with SiO2 as the support,Cs as the active component and Nb,V or P as the active additives.Effects of types of active additives and Cs contents(m(Cs)/m(support))on the crystal structures,acidities and alkalinities and textural properties of the catalysts were investigated by XRD,TPD and N2 adsorption/desorption,and the catalytic performances and stabilities of the catalysts in aldol condensation to MMA were also studied.The results show that under the conditions of n(formaldehyde):n(methyl propionate)of 1:3,temperature of 340℃,pressure of 0.2 MPa and raw material feed rate of 0.2 mL/min for 48 h,the catalyst with Cs content of 10.0%(Cs10.0-Nb/SiO2)demonstrates excellent catalytic performance,with the product(MMA+methacrylic acid)selectivity of 93.4%and the product yield of 21.3%.After selectively covering strong acid sites with NH3 and reacting for 96 h,the product yield and product selectivity of Cs10.0-Nb/SiO2 are 20.2%and 91.5%,respectively,slightly better than the original Cs10.0-Nb/SiO2.