金属组分负载量对Cu-Mn-Zn/Y直接合成二甲醚催化剂的影响

Effect of the content of metallic component on Cu-Mn-Zn/Y catalysts for direct synthesis of DME

通过对不同金属负载量Cu-Mn-Zn/Y催化剂的研究,结果发现,金属组分的负载量为30 mmol时,CO的转化率和二甲醚的选择性分别可达65.6%和67.0%。金属组分负载量20 mmol^30 mmol时,催化剂中各金属组分均呈高分散状态,增加金属组分负载量主要是增加了催化剂吸附CO和H2活性中心的数目,使得催化剂对CO的转化能力增加。当金属组分负载量达到35 mmol时,催化剂的微观结构发生了改变,作为主要活性组分的铜也发生了聚集,造成催化剂对CO和H2吸附能力降低;由于作为酸性组分的分子筛含量相对减少和大量金属组分对酸中心的覆盖作用,导致催化剂酸性降低,使得催化剂对CO的转化率和对二甲醚的选择性均降低。

The Cu-Mn-Zn/Y catalysts with the different content of metallic component were prepared through a coprecipitation impregnation method, and used for the synthesis of dimethyl ether （DME） from synthesis gas in a fixed-bed reactor. The optimum content of metallic component loading on per gram zeolite Y was about 30 mmol, and the conversion of CO and the selectivity of DME were 65.6% and 67.0% under 2.0 MPa, 245 ℃ and 1 500 h^-1. XRD, BET and TPD of H2, CO and NH3 results showed that, with the metal content increasing from 20 mmol to 30 mmol, the dispersion of all metallic component became better, the adsorption ability of H2 and CO also increased, but the surface area and the acidity of these catalysts did not changed. As the metal content up to 35 mmol, the accumulated copper and micro-structural changes occurred, the surface area of the catalysts and the adsorption ability of H2 and CO decreased rapidly, the number and strength of acid sites also decreased. Consequently, the Cu-Mn-Zn/zeolite-Y catalyst with 30 mmol metal loading exhibited the best catalytic performance for direct synthesis of DME was duo to the favorable adsorption ability of H2 and CO.