沉淀温度对K-CuLaZrO_2催化剂上合成气直接合成异丁醇的影响

合成气制备异丁醇是一个非常复杂的过程,催化剂性质与异丁醇形成之间的关系仍未完全理解。共沉淀法是合成固体复合氧化物常用的制备方法,分散度高、相互作用强、制备工艺简单,但是影响制备过程的因素很多。本研究深入考察沉淀反应开始时沉淀温度对催化剂性质的影响,进而通过不同的表征手段,结合评价结果建立催化剂性质与异丁醇形成的联系,进一步完善异丁醇形成机制。结果表明,低温(30℃)有利于CuO-ZrO_2固溶体的形成,两者分散性好,且彼此之间相互作用较强,有利于氧化铜还原。同时,在低温下,催化剂表面含有较多的羟基,与CO反应后形成较多的表面C_1物种,促进了碳链增长,提高了异丁醇选择性。提高沉淀温度后,CuO颗粒粒径增大,CuO-ZrO_2固溶体逐渐被破坏,两者相互作用减弱,且表面羟基含量降低,导致表面C_1物种减少,异丁醇选择性明显降低。在CLZ-30(沉淀温度为30℃)催化剂上,异丁醇的选择性最高可达38.7%。

Effect of precipitation temperature on the performance of K-CuLaZrO2 catalyst for isobutanol synthesis from syngas

The synthesis of isobutanol from syngas is a such complicated process, and the relationship between catalyst properties and isobutanol formation is still not fully understood yet. Coprecipitation is a common preparation method for solid composite oxides synthesis, by which, the catalyst will have high dispersion, strong interaction. However, it also remains many factors affecting the preparation process. In this work, the effect of precipitation temperature on the properties of catalysts at the beginning of precipitation reaction was investigated, and the relationship between the properties of catalysts and the formation of isobutanol was studied by different characterization methods in combination with the catalysts evaluation results, in order to further improve the formation mechanism of isobutanol. The results revealed that at lower precipitation temperature (30 ℃), the CuO was easier to be reduced due to the better Cu dispersion and stronger interaction in CuO and ZrO₂, at the same time as the CuO and ZrO₂ could form better solid solutions at this condition. Meanwhile, hydroxyl groups were formed on the catalyst surface at lower precipitation temperature during the catalyst preparation process, therefore these hydroxyl groups could react with CO to form surface C₁ species, which further promoted the growth of carbon chain and improved the selectivity of isobutanol. With the increase of precipitation temperature, CuO particles were enlarged; CuO-ZrO₂ solid solution was gradually destroyed; the interaction in CuO and ZrO₂ was weakened; and the content of surface hydroxyl was decreased, resulting in a decrease of surface C₁ species and isobutanol selectivity. Among all the catalysts, the highest selectivity of isobutanol (38.7%) was obtained over the CLZ-30 catalyst.