Propylene epoxidation with O2 to propylene oxide is a very valuable reaction but remains as a long-standing challenge due to unavailable efficient catalysts with high selectivity. Herein, we successfully explore 27 nm-sized cubic Cu2O nanocrystals enclosed with {100} faces and {110} edges as a highly selective catalyst for propylene epoxidation with O2, which acquires propylene oxide selectivity of more than 80% at 90–110 °C. Propylene epoxidation with weakly-adsorbed O2 species at the {110} edge sites exhibits a low barrier and is the dominant reaction occurring at low reaction temperatures, leading to the high propylene oxide selectivity. Such a weakly-adsorbed O2 species is not stable at high reaction temperatures, and the surface lattice oxygen species becomes the active oxygen species to participate in propylene epoxidation to propylene oxide and propylene partial oxidation to acrolein at the {110} edge sites and propylene combustion to CO2 at the {100} face sites, which all exhibit high barriers and result in decreased propylene oxide selectivity.

Fundamental understanding of complex FT synthesis is of great interest. We have employed X-ray photoelectron spectroscopy and temperature-programmed desorption to comparatively investigate CH 2 I 2 adsorption and reactions on clean, hydrogen-and CO-covered Co(0001) surfaces. Surface chemistry of CH 2 I 2 was demonstrated to sensitively depend on available vacant surface sites on Co(0001). Upon adsorption on clean Co(0001) surface at 110 K, CH 2 I 2 undergoes stepwise decomposition reactions to produce carbon adatoms, CH(a) and CH 2 (a) species at small coverages, and chemisorbs both dissociatively and molecularly at large coverages. Upon heating, CH 2 (a) species facilely undergoes surface reactions to produce CH 4 , C 3 H 6 , and C 2 H 4 in gas phase and CH(a) species on the surface at low temperatures. CH(a) species undergoes surface reactions to produce CH 4 in gas phase and C 2 H 2 (a) species on the surface at higher temperatures, and both CH(a) and C 2 H 2 (a) species undergo further surface reactions to produce H 2 in gas phase and carbon species on the surface. Coadsorbed H adatoms and CO molecules were found to strongly affect surface chemistry of CH 2 I 2 and the resulting CH x species on Co(0001) via suppressing the decomposition reactions and promoting the carbon− carbon bond coupling reactions. These results add novel insights in fundamental understanding of complex FT synthesis.

Investigating the surface chemistry of formaldehyde on the surface of TiO 2 is important in understanding the thermalcatalytic and photocatalytic reactions of formaldehyde on TiO 2involved catalysts. By combining thermal desorption spectroscopy and X-ray photoelectron spectroscopy, we studied the adsorption, thermo-induced surface reactions, and photo-induced surface reactions of formaldehyde on the rutile TiO 2 (011)-(2 × 1) surface. The dominant thermal-catalytic reaction is the formation of ethylene by a reductive carbon−carbon formation reaction of formaldehyde adsorbed at the oxygen vacancy sites, and the dominant photocatalytic reaction is the formation of formate, assisted by the bridge O 2c sites, followed by carbon monoxide formation at elevated temperatures. The surface intermediates of formaldehyde reactions to ethylene and carbon monoxide on the rutile TiO 2 (011)-(2 × 1) surface were identified. The effect of the surface structure of the rutile TiO 2 (011)-(2 × 1) surface, particularly the oxygen vacancy, on the thermal-catalytic and photocatalytic activity toward formaldehyde was revealed by studying the coadsorption of water and formaldehyde. These results broaden our fundamental comprehension on the reaction mechanism of formaldehyde on the TiO 2 surfaces.