Theoretical investigation of the decarboxylation and decarbonylation mechanism of propanoic acid over a Ru(0 0 0 1) model surface

Abstract

a b s t r a c tThe hydrodeoxygenation of organic acids is often found to be a rate-controlling process during upgrading of biomass feedstocks into fuels. We developed a microkinetic model based on data obtained from density functional theory calculations for the decarboxylation and decarbonylation mechanisms of propanoic acid (CH 3 CH 2 COOH) over a Ru(0 0 0 1) model surface. The model predicts that the decarbonylation mechanism is two orders of magnitude faster than the decarboxylation mechanism. The most favorable decarbonylation pathway proceeds via removal of the acid -OH group to produce propanoyl (CH 3 CH 2 CO) followed by C-CO bond scission of propanoyl to produce CH 3 CH 2 and CO. Finally, CH 3 CH 2 is hydrogenated to CH 3 CH 3 . Dehydrogenation reactions that have been observed to be important over Pd catalysts play no role over Ru(0 0 0 1), and a sensitivity analysis indicates that removal of the acid -OH group is the rate-controlling step in the deoxygenation. Overall, our results suggest that to improve the Ru catalyst performance for the decarbonylation of organic acids, the free site coverage needs to be increased by, for example, adding a catalyst promoter that decreases the hydrogen and CO adsorption strength (without significantly affecting the C-OH bond scission rate), or by raising the reaction temperature and operating at relatively low CO and H 2 partial pressures.

Insights into the mechanism of nitrobenzene reduction to aniline over Pt catalyst and the significance of the adsorption of phenyl group on kinetics

“…To model the mechanism of nitrobenzene reduction, there are two significant problems to overcome. The first challenge is associated with the large size of nitrobenzene molecule, because a larger molecule would considerably increase the number of possible adsorption configurations [21][22][23][24][25][26][27][28][29][30][31][32], therefore, a significantly more adsorption configurations should be carefully tested in the calculations of nitrobenzene, in contrast to the much fewer adsorption configurations of other smaller organic molecules such as formic acid or methanol. In addition, an increase in adsorption configurations would also lead to an increase in the numbers of possible transition states, which again makes the calculations more complicated and time-consuming [21,22].…”

“…Only a few pioneering works have been made in the study of these large molecules [21,22,[26][27][28][29][30][31][32]. Saeys et al calculated benzene adsorption and hydrogenation to cyclohexane on Pt(111) [21,22].…”

“…Mahata et al reported the mechanism of nitrobenzene reduction over Ni(111) via direct or indirect mechanisms [26]. With respect to some other large molecules in heterogeneous catalysis, Lu et al systematically calculated the hydrogenation of guaiacol over Ru(0001) and Pt(111) surfaces involving the C-O bond dissociation [28,29]. Wang et al studied the activity and selectivity between hydrogenation and decarbonylation of furan and its derivatives on Pd(111) [30,31].…”

Valorization of Biomass‐derived Small Oxygenates: Kinetics, Mechanisms and Site Requirements of H2‐involved Hydrogenation and Deoxygenation Pathways over Heterogeneous Catalysts

“…For example, distinguishing decarbonylation from decarboxylation pathways is experimentally challenging often due to the water gas shift (WGS) reaction occurring under HDO conditions. DFT assessments of the propanoic acid HDO on Pd(111),, Pd(211),, and Ru(0001) surfaces informed that decarbonylation is always the favored pathway on these surfaces under gas‐phase reaction conditions, irrespective of the prevalent H 2 pressures. Moreover, the catalytic activity of active sites on flat surface models was predicted by microkinetic modeling to be higher than that of stepped surface models by a factor of 3–8, suggesting that the HDO of propanoic acid over a Pd catalyst is moderately sensitive to the surface structure.…”

Effect of Surface Composition and Structure of the Mesoporous Ni/KIT-6 Catalyst on Catalytic Hydrodeoxygenation Performance

“…The research and development of high performance catalytic materials is the core of the HDO technology. At present, the most widely used catalytic materials are the supported noble metal catalysts, such as Pt [10], Pd [11], Ru [12], and so on. Pd/C catalyst has high yield of alkane products, which are used in the stearic acid HDO reaction.…”