Density Functional Theory Study of Acetaldehyde Hydrodeoxygenation on MoO3

Periodic spin-polarized density functional theory calculations were performed to investigate acetaldehyde (CH 3 CHO) hydrodeoxygenation on the reduced molybdenum trioxide (MoO 3 ) surface. The perfect O-terminated α-MoO 3 (010) surface is reduced to generate an oxygen defect site in the presence of H 2 . H 2 dissociatively adsorbs at the surface oxygen sites forming two surface hydroxyls, which can recombine into a water molecule weakly bound at the Mo site. A terminal oxygen (O t ) defect site thus forms after water desorption. CH 3 CHO adsorbs at the O-deficient Mo site via either the sole O−Mo bond or the O−Mo and the C−O double bonds. The possible reaction pathways of the adsorbed CH 3 CHO with these two configurations were thoroughly examined using the dimer searching method. Our results show that the ideal deoxygenation of CH 3 CHO leading to ethylene (C 2 H 4 ) on the reduced MoO 3 (010) surface is feasible. The adsorbed CH 3 CHO first dehydrogenate into CH 2 CHO by reacting with a neighboring terminal O t . The hydroxyl (O t H) then hydrogenates CH 2 CHO into CH 2 CH 2 O to complete the hydrogen transfer cycle with an activation barrier of 1.39 eV. The direct hydrogen transfer from CH 3 CHO to CH 2 CH 2 O is unlikely due to the high barrier of 2.00 eV. The produced CH 2 CH 2 O readily decomposes into C 2 H 4 that directly releases to the gas phase and regenerates the O t atom on the Mo site. As a result, the reduced MoO 3 (010) surface is reoxidized to the perfect MoO 3 (010) surface after CH 3 CHO deoxygenation.