Uniform Catalytic Nanocrystals: From Model Catalysts to Efficient Catalysts

Abstract

Conspectus Solid catalysts play a key role in the chemical industry, energy, and the environment. Fundamental understanding of heterogeneous catalysis exerted by solid surfaces is useful for structural designs of efficient catalysts but is challenging due to the complexity. Emerging uniform catalytic nanocrystals (NCs) with controlled and well-defined surface structures have brought new opportunities for fundamental understanding and directed explorations of efficient catalysts. In a previous Account (Acc. Chem. Res.201649520527), I postulated and exemplified a concept of oxide nanocrystal model catalysts for the fundamental investigations of oxide catalysis without the “materials gap” and “pressure gap” which are often encountered using the traditional single crystal model catalysts. In this Account, I summarize our effort in fabricating efficient uniform nanocrystal catalysts based on the fundamental understanding of structure–activity relations and reaction mechanisms acquired by oxide nanocrystal model catalyst studies. Directed by the fundamental understanding that the Cu2O{110} facet is active in catalyzing propylene epoxidation with O2 and the fine Cu2O nanocube exposes high densities of Cu2O{110} edge sites, we successfully explore fine Cu2O nanocubes as a highly selective catalyst for propylene epoxidation with O2. Directed by the fundamental understanding that the Cu{100} facet is the active Cu facet in catalyzing the water–gas shift (WGS) reaction, we successfully fabricate a highly active ZnO/fine Cu nanocube WGS catalyst with enhanced ZnO-CuCu{100} active site density. Directed by the fundamental understanding of TiO2 facet effects on the surface band bending and adsorbate–surface interfacial energy level alignment, and consequent photocatalytic performance, we successfully fabricate highly active TiO2{001} NC-based photocatalysts for photocatalytic CH4 conversions. These results adequately exemplify the concept of fundamental understanding-directed explorations of efficient catalysts following a strategy of “identification of active site structure + maximization of active site density”, which, together with the advancement of controlled-synthesis methods, is expected to greatly accelerate the explorations of novel and efficient catalysts in future.

Investigating the mechanism of propylene epoxidation over halogen (X = F, Cl, Br, I) modified Cu2O(110) surfaces: a theoretical study

“…[12][13][14][15][16] Yet, the complex network of reactions in DEP often precludes Cu or Cu 2 O catalysts from reaching optimal activity and selectivity by themselves. [17][18][19] In this regard, the introduction of organic and inorganic additives would open new dimensions to optimize the catalytic performance. Specifically, halogens such as fluorine (F), chlorine (Cl), bromine (Br), and iodine(I) ions have proven to be exceptionally effective modulators of catalyst behaviours for olefin epoxidation.…”

Cu Facet-Dependent Elementary Surface Reaction Kinetics of CO2 Hydrogenation to Methanol Catalyzed by ZrO2/Cu Inverse Catalysts

“…Atomically dispersed Cu–O–Zr sites were reported to exclusively catalyze the reverse water gas-shift (RWGS) (CO 2 (g) + H 2 (g) = CO­(l) + H 2 O­(l)) reaction, whereas the monatomic dispersed Cu 1 /ZrO 2 catalyst achieved 100% methanol selectivity in CO 2 hydrogenation . CO 2 hydrogenation to methanol over ZrO 2 –Cu based catalysts was proposed via the RWGS+CO-Hydro pathway or formate pathway. ,,, Additionally, the phase of ZrO 2 also profoundly affected the catalytic performance of ZrO 2 –Cu-based catalysts in CO 2 hydrogenation. ,,− The Cu facet was extensively reported to influence the catalytic performance of Cu-involved catalysts − but has not been reported for ZrO 2 –Cu catalysts in the CO 2 hydrogenation reaction. Meanwhile, we found that temporal in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was able to study elementary surface reaction kinetics of catalytic reactions involving stable surface intermediates, such as formate species during CO or CO 2 hydrogenation reactions .…”