Density-functional theory studies of acetone and propanal hydrogenation on Pt(111)

Abstract

Self-consistent periodic slab calculations based on gradient-corrected density-functional theory ͑DFT-GGA͒ were conducted to probe the potential-energy diagram for the hydrogenation of propanal and acetone on Pt͑111͒. Calculations for molecularly adsorbed species indicate that acetone and propanal are both weakly bound to the surface through oxygen ͑i.e., energy changes of adsorption near Ϫ20 kJ/mol͒. The activation energy barriers are calculated to be ϳ60 and 40 kJ/mol for the addition of an adsorbed hydrogen atom to adsorbed acetone and propanal, leading to adsorbed isopropoxy and n-propoxy species, respectively. The subsequent hydrogenation steps to form adsorbed alcohol species have activation barriers near 15 kJ/mol. These results would suggest that the rate of propanal hydrogenation over Pt should be faster compared to acetone hydrogenation, in contrast to the behavior observed experimentally ͓G.M.R. van Druten and V. Ponec, Applied Catalysis A: General 191, 153 ͑2000͔͒. The origin for the experimentally observed slower rate of propanal hydrogenation over Pt appears to be related to the formation of strongly adsorbed spectator species formed by removal of the ␣-H atom from adsorbed propanal. The calculated energy change for cleavage of this C-H bond, leading to adsorbed propionyl and adsorbed hydrogen atom, is exothermic by 76 kJ/mol.

Reforming of Oxygenates for H2 Production on 3d/Pt(111) Bimetallic Surfaces

“…Overall, the size of the species had a relatively small effect on the binding energy, as the values for different molecular oxygenates and alkoxide species were similar. These results are in agreement with previous DFT studies of methanol and methoxy on Pt(111) [59,60,61] and Ni(111) [62,63], and ethanol and ethoxy on Pt(111) [64].…”

Experimental and DFT Studies of the Conversion of Ethanol and Acetic Acid on PtSn-Based Catalysts

“…In a previous study, we have identified various transition states for cleavage of C-O and C-C bonds in species derived from ethanol on Pt(111). 20 In that study we employed a strategy in which transition states were first identified for reactions that have favorable thermodynamics. A correlation was then developed for the energies of these transition states in terms of the energies of the corresponding final states, and this correlation was used to estimate the energies of transition states for other C-O and C-C bond cleavage reactions.…”

“…C 2 H 6 ) on Pt(111). 20 Indeed, experimental studies show that ethanol reacts on Pt at 500 K to give CO, CH 4 , and C 2 H 6 by cleavage of C-O and C-C bonds. 21 Thus, it is necessary to inhibit these decomposition reactions if Pt-based catalysts are to be used for selective conversions of oxygenated hydrocarbons.…”

The ethanol electrooxidation at Pt layers deposited on polycrystalline Au

“…According to Dumesic and co-workers 34 the transition state for the C-C bond breaking directly from ethanol or from the acetaldehyde precursor over a Pt(111) surface has similar energies (1.5 eV). However, the most stable precursor indicated as responsible for the C-C rupture is the CHCO species.…”