ZrO_(2)晶型对CO加氢制异丁烯反应影响的研究

Effect of crystal structure of ZrO_(2)catalyst on isobutene synthesis from CO hydrogenation

不同晶型结构的ZrO_(2)在CO加氢制异丁烯反应中表现出不同的催化性能。尽管单斜相ZrO_(2)在合成气制异丁烯反应中具有最优异的催化性能,但是对于其异构化活性位仍缺乏深入认识。通过研究ZrO_(2)晶型结构对反应性能的影响差异,有利于深入认识ZrO_(2)催化剂上合成气制异丁烯反应的关键影响因素。因此,本研究制备了一系列不同晶型结构的ZrO_(2)催化剂,研究了它们在结构性质及催化CO加氢制异丁烯反应性能方面的差异。相对于四方相和无定型ZrO_(2),在单斜相ZrO_(2)催化剂表面,有较多的配位不饱和的Zr位点和O位点。配位不饱和的Zr位点是CO吸附活化的位点,有利于CO的转化。而较多的不饱和配位的O位点,为异丁烯的生成提供了更多的碱性位。此外,在单斜相ZrO_(2)催化剂表面,配位不饱和的Zr位点和O位点的存在,抑制了电子向反应中生成的甲酸盐物种转移,因此,甲酸盐物种在催化剂表面吸附较弱,有利于CO加氢生成异丁烯。

ZrO_(2)catalysts with different crystal structures show different catalytic performance in isobutene synthesis from CO hydrogenation reaction.Although monoclinic ZrO_(2)has the best catalytic performance in isobutene synthesis from syngas,its isosynthesis active sites are still not well understood.To better understand the critical parameters that influence syngas to isobutene reactions over ZrO_(2)catalysts,we prepared a series of ZrO_(2)catalysts with distinct crystal structures and investigated their catalytic performance of CO hydrogenation to isobutene.Compared with tetragonal and amorphous ZrO_(2)catalysts,there are more coordinatively unsaturated Zr and O sites on the surface of monoclinic ZrO_(2)catalyst.The coordinatively unsaturated Zr sites are the active sites of CO adsorption and activation,which is beneficial to CO conversion.The coordinatively unsaturated O sites provide more basic sites for isobutene formation.Furthermore,the coordinatively unsaturated Zr and O sites on monoclinic ZrO_(2)catalyst surface may inhibit electron transfer to formate species formed during reaction,resulting in weak adsorption on catalyst surface of formate species.The weakly adsorbed formate species on the surface of monoclinic ZrO_(2)catalyst is favorable for the synthesis of isobutene from CO hydrogenation reaction.