Unraveling the mechanism of propanoic acid hydrodeoxygenation on palladium using deuterium kinetic isotope effects

Solvent effects in the liquid phase hydrodeoxygenation of methyl propionate over a Pd(1 1 1) catalyst model

“…We focus on Pd (111) surface sites since Pd catalysts have previously been studied by us experimentally and computationally and are generally known to be quite active for the HDO of organic ester and acids. [4][5][6][23][24][25][26] Also, we identified the (111) surface to be the main active site for the HDO of organic acids over Pd/C catalysts. 25 After investigating the effect of these solvents on the free energies of all elementary steps in the reaction mechanism, we developed a mean-field microkinetic model to study the effects of these solvents on the overall reaction kinetics and mechanism of the HDO of methyl propionate.…”

An efficient hydrogenation catalytic model hosted in a stable hyper-crosslinked porous-organic-polymer: from fatty acid to bio-based alkane diesel synthesis

“…From literature, the process of alkane formation may involve three different routes. 19,30,70,82,83 The first pathway is the initial hydrogenation of fatty acid to alcohol along with the subsequent hydro-dehydration and produces the corresponding alkane with the same number of carbon as the initial fatty acid. The other two remaining routes involves the direct decarboxylation pathway (CO2 removal) of fatty acid and the decarbonylation pathway (CO removal), both produce the alkane with one carbon less in the hydrocarbon chain.…”

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

“…argued that dehydrogenation of the α‐carbon (C−H bond scission) in the acid‐derived intermediate should be the RDS at low H 2 pressures, while the kinetic relevance of C−OH cleavage increased at higher H 2 pressures, for both Pd(111) and Pd(211) surfaces . In a later experimental investigation, deuterium KIE values were measured for the atmospheric‐pressure HDO (to ethane) of propanoic acid (CH 3 CH 2 COOH/CH 3 CD 2 COOH) on Pd/C catalysts at relatively high (20 kPa; KIE=1.1) and low (5 kPa; KIE=1.6) H 2 pressures at 473 K, qualitatively in accord with the expectation of a primary KIE associated with a C−H(D) bond cleavage RDS . A more detailed microkinetics treatment predicted a KIE of 1.5 at 5 kPa H 2 and 1 kPa acid, in closer agreement with the measured values.…”

“…The computational description of solvent molecules in a catalytic system can be done with implicit or explicit treatments ,. Steinmann et al.…”

“…Using the implicit solvation model, Heyden and coworkers studied the effects of polar solvents such as water, n‐butanol (protic) and 1,4‐dioxane (aprotic), as well as nonpolar solvents such as n‐octane, on the elementary steps involved in the HDO of propanoic acid, and they utilized a microkinetic model to quantify the effects of solvent molecules on the reaction rates and other kinetic parameters over Pd(111) and (211) surfaces. They found that nonpolar solvents did not change the HDO kinetics compared to gas‐phase results, while the polar molecules like water altered the overall activity and even the mechanism (e. g., toward more decarboxylation instead of decarbonylation over Pd (111) and the stepped (211) surfaces,). Their results also showed that in all reaction environments and along the decarbonylation pathway, C−OH bond cleavage is the most rate‐controlling step at medium H 2 pressures (∼1 bar), with dehydrogenation steps of propanoic acid and propionate being significantly facilitated (apparent activation barrier decreases in by up to 0.16 eV) in the presence of water.…”