Iyemperumal Satish Kumar, Deskins N Aaron
Department of Chemical Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts 01609, USA.
Phys Chem Chem Phys. 2017 Nov 1;19(42):28788-28807. doi: 10.1039/c7cp05718k.
Catalytic reduction of carbon dioxide to useful chemicals is a potent way to mitigate this greenhouse gas, but the challenge lies in finding active reduction catalysts. Using density functional theory we studied CO activation over TiO-supported Cu clusters of size 1-4 atoms. The linear to bent transformation of CO is necessary for activation, and we found that all the clusters stabilized bent CO, along with a significant gain of electrons on the CO (indicative of activation). On all the TiO supported Cu clusters, the interfacial sites were found to stabilize the bent CO adsorption, where the active site of adsorption on Cu dimer, trimer and tetramer was on the Cu atom farthest away from the TiO surface. Particularly, the Cu dimer stabilized bent CO very strongly, although this species was found to be unstable on the surface. A synthesis technique that could stabilize the Cu dimer could therefore lead to a very active catalyst. Furthermore we found (using vibrational and charge analysis) that the active sites for the CO activation predominantly had 0 and +1 oxidation states; the oxidation state of Cu is known to directly affect CO reduction activity. Our study shows TiO-supported small Cu clusters can be active catalysts for CO reduction and also provides further motivation for theoretical and experimental studies of metal clusters.
将二氧化碳催化还原为有用的化学品是减轻这种温室气体影响的有效方法，但挑战在于找到活性还原催化剂。我们使用密度泛函理论研究了尺寸为1 - 4个原子的TiO负载的Cu簇上的CO活化。CO从线性到弯曲的转变对于活化是必要的，我们发现所有的簇都使弯曲的CO稳定化，同时CO上有显著的电子增益（表明活化）。在所有TiO负载的Cu簇上，发现界面位点能稳定弯曲的CO吸附，其中在Cu二聚体、三聚体和四聚体上的吸附活性位点位于离TiO表面最远的Cu原子上。特别地，Cu二聚体非常强烈地稳定弯曲的CO，尽管这种物种在表面上被发现是不稳定的。因此，一种能够稳定Cu二聚体的合成技术可能会产生一种非常活性的催化剂。此外，我们发现（使用振动和电荷分析）CO活化的活性位点主要具有0和 +1氧化态；已知Cu的氧化态直接影响CO还原活性。我们的研究表明TiO负载的小Cu簇可以是用于CO还原的活性催化剂，也为金属簇的理论和实验研究提供了进一步的动力。
