载体H+含量对CuY甲醇氧化羰基化反应性能影响

通过过量浸渍Cu(NO_3)_2溶液于Y分子筛载体上,制备出Cu负载量为6.4%的CuY催化剂,考察了甲醇氧化羰基化反应的催化性能,并采用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、透射电子显微镜(TEM)和NH3程序升温脱附(NH3-TPD)等手段对催化剂表面微观结构进行了表征。研究表明,随Y分子筛载体H+含量的增加,可使更多Cu物种落位于分子筛微孔笼结构中,且高度分散,而笼内未交换的Na+能进一步促进铜物种更多落位于载体超笼结构中,形成更多甲醇氧化羰基化反应的Cu+活性中心。同时随铜物种引入,催化剂中产生了明显的中强酸,酸量随落位于载体笼结构中的Cu物种的增加而增加,催化剂总酸量随之增加,导致甲醇氧化羰基化产物分布发生改变,碳酸二甲酯(DMC)选择性明显降低。对比等体积浸渍法制备的92.3%的高DMC选择性CuY催化剂,以不含H+的NaY分子筛为载体,过量浸渍法制备的CuY催化剂酸量少、Cu物种活性中心多,在保持82.4%的高DMC选择性时,其DMC的时空收率(STY)也高达109.1mg·g~(-1)·h-1。

Influence of H+ Contents of Support on CuY Catalyst for Catalytic Performances of Oxidative Carbonylation of Methanol

A series of Y zeolite supported Cu catalysts (CuY) with Cu loading of 6.4% were prepared by wet impregnation method and investigated in oxidative carbonylation of methanol. The microstructure and surface properties of the catalysts were characterized by X-ray diffraction (XRD), H₂-temperature program reduction (H₂-TPR), NH₃-temperature program desorption (NH₃-TPD), transmission electron microscope(TEM) techniques. With the increase of H⁺ content, the Y zeolite supports were more conductive to the cation exchangment with Cu²⁺, leading to well dispersed Cu species in cages. Above all, the non-exchanged Na⁺ of Y zeolite resulted in more Cu species located in the super cages. After calcination, the copper species converted into Cu+, which enhanced the catalytic activity of oxidative carbonylation of methanol. The introduction of Cu species into Y zeolite produced moderate acid sites and the amount of acid was also increased with the increase of Cu species located in the cages, As a result, the reaction product distribution varied and the selectivity of DMC decreased with the increase of H⁺ content. The CuY catalyst prepared by incipient-wetness impregnation method gave 92.3% selectivity of DMC, whereas the Cu catalyst supported on NaY zeolite by wet impregnation method gave 82.4% selectivity of DMC and high space-time yield (STY) of DMC, 109.1 mg·g^-1·h^-1.