Mechanistic Pathways for Methylcyclohexane Hydrogenolysis over Supported Ir Catalysts

Abstract

H/D isotope effects on methylcyclohexane hydrogenolysis over Ir/Al 2 O 3 catalysts were examined by combining measured rates with theoretical estimates provided by partition function based analyses. Normal H/D isotope effects (r H /r D > 1) were observed for endocyclic and exocyclic C−C bond hydrogenolysis. Hydrogenolysis is concluded to occur via stepwise dehydrogenation followed by cleavage of the C−C bond and subsequent hydrogenation of the cleaved entities. The so-called "multiplet" mechanism (i.e., the C−C bond of a flat-lying physisorbed cyclic molecule is cleaved upon the attack of a coadsorbed H atom) is unequivocally excluded. For ring-opening, either C−C bond cleavage or C−H(D) bond reformation may be rate-determining, due to their indistinguishable isotope effects under the studied conditions. C−H(D) bond dissociation does not control the rate of C−C bond hydrogenolysis. For the exocyclic cleavage of the methyl group, a higher degree of unsaturation of the surface intermediate and the potential impact of mobile H atoms on large Ir particles are noted.

Disordered, Sub-Nanometer Ru Structures on CeO2 are Highly Efficient and Selective Catalysts in Polymer Upcycling by Hydrogenolysis

“…Figure b shows the PP conversion rate normalized to exposed Ru, that is, the intrinsic activity of Ru, plotted against Ru loading. In the high-loading range, the intrinsic activity decreases when the particle size decreases, consistent with the common observation in the literature that the turn-over-frequency (TOF) of gas-phase alkane hydrogenolysis is lower on smaller metal particles as low-index flat planes are required for alkane adsorption. − On the contrary, the opposite trend was observed in the low-loading range, that is, the intrinsic activity increases drastically when particle size decreases. With the high Ru dispersion and high intrinsic activity, the catalytic efficiency of ≤0.125 wt % Ru/CeO 2 , gauged by PP conversion rate per total Ru (110 g PP·h –1 ·g Ru –1 , Table S1), exceeds previous results by almost an order of magnitude (Table S1).…”

Ir@Pt bimetallic overlayer catalysts for aqueous phase glycerol hydrodeoxygenation

“…The catalyst was loaded into a quartz tube to be calcined in near stagnant air at 400°C for 3 h using a 3°C/min ramp rate up and down. After calcination the catalyst was reduced in 10 sccm H 2 flow at 500°C for 3 h using a 3°C/min ramp rate for the total reduction of Ir particles [30]. Multiple overlayer depositions were done by repeating the above procedure to produce single, double, and triple deposition Ir@Pt samples, denoted as Ir@Pt SD, Ir@Pt DD, and Ir@Pt TD, respectively.…”

Effect of reaction conditions on the hydrogenolysis of polypropylene and polyethylene into gas and liquid alkanes

“…25,27 These differences are typical for hydrogenolysis of alkanes varying in size; that is, the structure sensitivity markedly decreases as the molecular size increases. 29,30…”