低CO2选择性的合成气制轻烯烃双功能催化剂

Bifunction catalyst for syngas to light olefins with low CO2 selectivity

摘要:

为开发高活性、高收率的合成气制低碳烯烃（STO）双功能催化剂，通过共沉淀法制备非化学计量尖晶石Zn-Cr-Al氧化物，对其织构性质、晶体结构、形貌特征以及表面电荷性质等进行研究。结果表明添加过量锌能够促进晶体粒径减小，表面氧空位增多。其中Zn/(Cr+Al)摩尔比为1.25时锌含量较为适宜，将其与SAPO-34沸石分子筛结合为双功能催化剂用于STO性能研究。在进气n(H2):n(CO)=2:1，3000 mL/(gcat·h)，3.2 MPa，400 ℃反应条件下，实现46.9% CO转化率，C2-4烯烃收率高达15.9%，高于大部分已有文献报道（8~14%），特别是副产物CO2选择性仅29.2%，低于普遍报道的40~50% CO2选择性。并且催化剂运行100 h后活性良好，稳定的催化性能使其具有工业应用价值。

关键词:CO转化;低碳烯烃;双功能催化;低CO₂选择性;氧空位

Abstract:

The non-stoichiometric spinel Zn-Cr-Al oxide (ZCA-1.25) was prepared by co-precipitation method in order to develop a high activity and high yield bifunctional catalyst for synthesis of light olefin from syngas (STO), and its texture, crystal structure, morphology and surface charge properties were investigated. The results show that the addition of excessive zinc promotes the reduction of crystal grain size and the increase of surface oxygen vacancies. The zinc content is suitable when the Zn/(Cr+Al) mole ratio is 1.25, with high specific surface area and abundant oxygen vacancies, which is combined with SAPO-34 zeolite molecular sieve as a bifunctional catalyst to evaluate the catalytic performance of STO reaction directly. Under the reaction conditions of inlet n(H2):n(CO)=2:1, 3000 mL/(gcat·h), 3.2 MPa, 400 ℃, the CO conversion of 46.9% was achieved, and the light olefin yield was as high as 15.9%, higher than most of the existing literature reports (8~12%), especially the selectivity of by-product CO2 was only 29.2%, lower than the commonly reported 40~50% CO2 selectivity. It also provides an insight into inhibiting CO2 selectivity to improve the yield of target products. In addition, the catalyst has good activity and no carbon deposition after running for 100 h, therefore the stable catalytic performance makes it have the potential for industrial application.

Key words:CO conversion; light olefins; bifunctional catalysis; low CO₂ selectivity; oxygen vacancies