Influences Of Crystal Size And Acidity Of Y Zeolite On CuY Catalyst For Oxidative Carbonylation Of Methanol

Dimethyl carbonate(DMC) is a green chemical, praised as the “new footstone” for organic synthesis, which was not only widely applicated in methylating agent and carbonylation agent, but also used as efficient-nontoxic solvent in paint and pharmaceutical industries. Among numerous theoretical synthesis lines of DMC, the vapor-phase oxidative carbonylation of methanol is one of the industrial and green synthetic routes, because of rich raw materials, quick and easy reaction, and high atomic economy with products of H2 O and DMC.While supported copper based catalysts gradually become the core of catalysts. Kinds of copper highly dispersed on the support, which contribute to the contact to reactants. So to improve the catalytic activity in the gas phase reactions. Y molecular sieve stands out by its good hydrothermal stability, large specific surface area, ordered microporous structure and more cationic sites formed, which was easier to ions exchanged with Cu2+and highly dispersed, improving the performance of the reaction. In conclusion, using Y zeolite as the support of Cu Y catalyst has been taken much attention to in related field.While the change of the zeolite properties often has a great influence on the catalytic reaction performance. The crystal size of Y molecular sieve decides the amounts and length of channels linked to outside. All of which are in favour of the ions exchanged, making Cu species dispersedly, and reactants contact with them to strengthen the catalytic reaction. In addition, the amounts of cation also directly decides the acidic properties and distribution. The different amounts of Cu2+ solid-ion-exchanged casued a variation of the dispersion, valence state of Cu species and acid characteristics of catalyst. In a word, crystal size and surface acidity of Y zeolite had a great influence on the catalytic activity in the gaseous oxidative carbonylation of methanol.This dissertation researches on the effects on Cu Y catalyst microstructure taken by different crystal size and different acidity of Y zeolite. The supports were gotten, through a good method of synthesizing different crystal size of Y zeolite without guiding agent by adding trace amounts of surfactant and and changing the cation contents(H+) of Y zeolite. The effects were mainly studied about Cu species, dispersion, valence state and acid amounts of Cu Y catalyst, morever, the relationship between catalysts and reaction. Combined with the characterization of the microstructure of catalysts, it founded a great influence on the catalytic activity of Cu Y catalyst with different crystal size and cation amounts of Y support. The conclusions are as follows:(1) When small and even spherical crystal of Na Y molecular sieve was synthesized without guiding agent but surfactant tween20, the key synthesis condition: The catalysts were prepared at lower temperature of 0℃ and ratio of n(H2O)/n(Si O2) to 12 were conducive to form the small crystal size of Y zeolite, the smaller size of Y zeolite was down to 0.3 μm, during the aging time give shorten obviously with the tween 20 adding.(2) Cu Y catalysts were prepared from Cu(NO3)2 solution and Y zeolites with different crystal size by wet impregnation method. When the crystal size was decreased from 3.0 μm to 0.3 μm, more Cu2+ exchanged to it and highly dispersed. Due to short microcellular structure and more pore windows interlinked to outsides of small crystal size of Y zeolite, which facilitated molecular diffusion and contaction between reactant and active sites, the conversion of methanol increased remarkably from 1.35% to 5.60%. While, DMC selectivity get decreased along with the total amounts of acid sites increased resulting from much more Cu2+ located in cages.Ultimately, the catalyst prepared by the 0.3 μm Y molecular sieve gave the highest DMC space-time yield, 165.4 mg?g-1?h-1.(3) Cu Y catalysts were prepared from Cu(NO3)2 solution and Y zeolite with different content of cation(H+) by wet impregnation method. When the content of H+ was up to 64%, more copper species located in cages of Y zeolite dispersedly, and the Na+ of Y zeolite which had not been exchanged would further promoted more Cu2+ to locate in the supercage of zeolite to form Cu+. which was conductive to the improvement of catalytic activity. space-time yield(STY)of DMC was up to 109.1mg?g-1?h-1. Morever, the content of moderate and total acidity increased as amount of Cu species located in cages of zeolites added, Which led to changes of product distribution, lowing DMC selectivity. Compared with Cu Y catalyst prepared by incipient-wetness impregnation method with 92.3% high selectivity of DMC, The Cu Y catalyst prepared by Na Y zeolite with less H+ still gave a high DMC selectivity of 82.4%.