Preparation And Catalytic Performance Of The Supported Bifunctional Magnetic Catalysts

Methanol is an important chemical raw material of C1. In recent years,there has been a phenomenon of excess production. The methyl formate (MF)is a kind of very important organic intermediates of downstream products of methanol, it not only can be directly used as smoke agent and bactericide of dry fruits, grains and so on, but it also can be used as a raw material of organic solvents and synthetic drugs, which has a very wide range of applications.As a catalyst support in the heterogeneous reaction system, the mesoporous materials have many advantages, such as steady pore structure and high adsorption capacity. In particular, the composite magnetic catalyst support is prepared by combining the mesoporous material and the magnetic Fe304. The composite material not only keeps the characteristics of separation and recovery under the magnetic field, but also maintains the characteristics of mesoporous materials. In this paper, the bifunctional catalysts for the catalytic synthesis of methyl formate by liquid phase catalytic oxidation of methanol were studied.γ-Al2O3 is firstly prepared by roasting pseudoboehmite in this paper, and noble metal nanoparticles Au, Pd were loaded on γ-Al2O3 by impregnation and reduction. Single metal Au/γ-Al2O3 , Pd/γ-Al2O3 and double metal Pd-Au/γ-Al2O3 catalyst were prepared. Also magnetic core Fe304 is coated with γ-Al2O3 by the hydrolysis of isopropanol aluminum and magnetic bifunctional catalysts were prepared, the catalyst were characterized by XRD,XPS, BET, NH3-TPD, H2-TPR, TEM and so on. The catalytic properties of the catalysts is characterized in methanol liquid phase catalytic system to methyl formate. The experimental results are as follows:(1) A series of Au/γ-Al2O3 catalysts were prepared by loading Au nanoparticles on the γ-Al2O3 support, the specific surface area and pore volume were 332.7 m2·g-1 and 1.14 cm3·g-1, and the distribution of Au nanoparticles was even with an average particle size of about 5nm, but the catalytic effect was not ideal in the liquid phase catalytic reaction. When the loading amount was lwt%, which in the reaction condition of 5 mL methanol,0.8 MPa oxygen pressure, 130℃ and 6 h, the conversion rate of methanol reached the maximum of 28.5% and the selectivity of methyl formate was about 37.15%, yield 10.59%. Join in the proper proportion of Pd in Au catalyst to prepare double metal Pd-Au/γ-Al2O3 catalyst. The catalyst surface area and pore volume were 353.5 m2·g-1 and 1.53 cm·g-1, with a particle size of 2～5 nm of the noble metal nanoparticles, also the catalyst acidity and oxidation are obviously improved compared with single metal Au/γ-Al2O3 catalyst. In methanol liquid phase catalytic conversion to methyl formate, it showed very good catalytic performance in the reaction system. And the catalytic activity and the selectivity of MF was obviously higher than that of Au/γ-Al2O3 catalyst. When the reaction temperature is 160℃, oxygen pressure 1.0 MPa,reaction time 6 h, the conversion rate of methanol and methyl formate selectivity are respectively about 53.47% and 58.45%, yield 31.25%.(2) Pd/γ-Al2O3 catalyst were prepared by the same preparation method as the Au/γ-Al2O3 catalyst, but its catalytic activity has been significantly improved. The oxidation and acidity are higher than that of Au/γ-Al2O3 catalyst, and the average size of Pd nanoparticles is about 5nm.The conversion rate of methanol can reach about 47.17%, methyl formate selectivity can reach 41.83%, yield 19.11% in the optimal the reaction conditions. At the same time,the magnetic bifunctional catalyst was prepared by hydrolysis of aluminum isopropoxide, which was characterized by XRD and VSM. The results show that the catalyst has good superparamagnetic properties and maintains the characteristic diffraction peaks of γ-Al2O3 and Fe304. Methanol conversion and methyl formate selectivity were 46.87% and 40.79%, the yield was 19.11% in the optimal reaction conditions, and the catalytic performance of Pd/γ-Al2O3@Fe3O4 did not change significantly compared to Pd/γ-Al2O3 catalyst, but the repeated use of performance significantly improved.