CuZnTiO2/SAPO-34双功能催化剂的设计、制备及其用于CO2加氢制烯烃性能

CO₂加氢经甲醇（含氧中间体）制低碳烯烃工艺路线，可实现成醇、脱水两步反应串联协同进行，打破费托合成产物Anderson-Schulz-Flory（ASF）分布限制，高选择性地制取低碳烯烃。传统甲醇合成Cu基催化剂加氢能力较强，在两步反应中产物以CH₄、低碳烷烃为主。实验设计、制备了CuZnTiO₂/(Zn-)SAPO-34复合催化剂，实现了CO₂加氢在Cu基复合催化剂上高选择性合成C₂～C₄烯烃（约60%）。研究表明，两步反应过程中甲醇体积分数较低（＜6%），且高温下逆水煤气变换反应严重，导致催化剂酸性变化对产物分布的影响较大。调变两类活性位点比例发现，CH₄的产生与串联反应存在竞争关系，SAPO-34酸量的增加抑制了CH₄的生成，促进串联反应正向进行；合适的酸性有助于生成C₂～C₄烯烃。控制成醇、脱水两类活性位点接触距离可调变烯烃的二次反应，降低加氢能力，改善产物分布。

Design and preparation of CuZnTiO2/SAPO-34 bifunctional catalyst and its catalytic performance in CO2 hydrogenation to light olefins

CO₂ hydrogenation to light olefins bymethanol synthesis or oxide intermediates, is accomplished through two successive reactions of activation of CO₂ to methanol and methanol conversion to olefins. This route can break the product distribution limitation of Anderson-Schulz-Flory (ASF) via Fischer-Tropsch synthesis and produce light olefins with high selectivity. It is reported that the products from traditional Cu-based composite catalysts mainly include methane and alkanes due to their strong hydrogenation ability during CO₂ hydrogenation. Herein, we report the design and preparation of CuZnTiO₂/(Zn-)SAPO-34 composite catalyst that shows high selectivity for C₂—C₄ olefins (around 60%). The study demonstrates that the acidity of the catalyst has great influence on product distribution, due to the low methanol concentration (＜6%) and high activity of the reverse water gas shift reaction (RWGS) at high temperature during the two-step reaction process. There exists competition between the formation of methane and the tandem reaction with the change of the content of two active components. The increase of the acid content of SAPO-34 can inhibit the formation of methane and promote the tandem reaction. Reduction in acidity of SAPO-34 by Zn promotion also contributes to the formation of light olefins. It is favorable to suppress the secondary hydrogenation reaction of light olefins, by controlling the distance between the two active components.