Modification Of CuY Catalyst For The Oxidative Carbonylation Of Methanol To Dimethyl Carbonate

As an important organic synthesis intermediate,dimethyl carbonate?DMC?is widely used in pesticides,pharmaceuticals,dyes and other aspects.Because of its low toxicity and pollution-free,it is known as“green chemicals”.Compared with the traditional production methods,such as conventional phosgene route,oxidative carbonylation of methanol to synthesize DMC has many advantages,such as attainable raw materials,by-products of water,relatively mild reaction conditions etc.CuY zeolite is an excellent oxidative carbonylation catalyst and it can avoid the atalyst deactivation and equipment corrosion caused by chlorine loss in the reaction system.In this paper,the effects of different CuY catalyst reduction methods on the form of Cu species and the structure modification etched by NH₄F solution were studied.CuY catalysts were prepared using cupric nitrate as the copper source by ammonia evaporation method.The effects of different pH value of copper ammonia complex solution were investigated,and two different reduction methods were adopted to restore and activate the catalysts?vapor-induced reduction of methanol and auto-reduction at high temperature?.It was found that the catalyst prepared by vapor-induced reduction of methanol and prepared by high pH value of copper ammonia complex solution had better catalytic activity.The space-time yield of optimal catalyst was as high as 268.6mg/(g_cat·h),the selectivity was 58.4%,and the conversion rate was 12.3%CuY zeolite contained a variety of copper sites,and the Cu localization of CuY catalysts prepared by different pH values of copper ammonia complex solution and different reduction methods were different.Through experiments and characterization,we found that the Cu⁺ion in site II was more conducive to the reaction,while the catalyst prepared by vapor-induced reduction of methanol and higher pH value of copper ammonia complex solution contained more Cu⁺ions in site II.Due to the small size of the sodalite cage in Y zeolite,the reactant molecules can hardly contact with the exchanged Cu sites in sodalite cages,and the Cu utilization efficiency is low.By using the NH₄F solution,Si atoms in the zeolite and Al can be removed at the same etching rate.The opening sodalite cages caused local defect on the surface of the Y zeolite,so that the reactant molecule?CO,methanol,etc.?can be contacted with the active sites in the small cages,thereby improving the catalytic reaction activity.With the increase of etching time,the catalytic activity appears to increase first and then decrease.This is because when the etching time is too long,the Al atoms in the molecular sieve are excessively removed and the B acid sites are reduced.As the sites decrease,the catalytic activity also decreases.The best etching time was 10 min.At this time,the maximum space-time yield of DMC was 436.2mg/(g_cat·h).