Role of the Support and Reaction Conditions on the Vapor-Phase Deoxygenation of m-Cresol over Pt/C and Pt/TiO₂ Catalysts

Abstract

The catalytic deoxygenation of biomass fast pyrolysis vapors offers a promising route for the sustainable production of liquid transportation fuels. However, a clear understanding of the mechanistic details involved in this process has yet to be achieved, and questions remain regarding the role of the catalyst support and the influence of reaction conditions. In order to gain insight into these questions, the deoxygenation of m-cresol was investigated over Pt/C and Pt/TiO 2 catalysts using experimental and computational techniques. The performance of each catalyst was evaluated in a packed-bed reactor under two conditions (523 K, 2.0 MPa and 623 K, 0.5 MPa), and the energetics of the ring hydrogenation, direct deoxygenation, and tautomerization mechanisms were calculated over hydrogen-covered Pt(111) and oxygen vacancies on the surface of TiO 2 (101). Over Pt(111), ring hydrogenation to 3methylcyclohexanone and 3-methylcyclohexanol was found to be the most energetically favorable pathway. Over TiO 2 (101), tautomerization and direct deoxygenation to toluene were identified as additional energetically favorable routes. These calculations are consistent with the experimental data, in which Pt/TiO 2 was more active on a metal site basis and exhibited higher selectivity to toluene at 623 K relative to Pt/C. On the basis of these results, it is likely that the reactivity of Pt/TiO 2 and Pt/C is driven by the metallic phase at 523 K, while contributions from the TiO 2 support enhance deoxygenation at 623 K. These results highlight the synergistic effects between hydrogenation catalysts and reducible metal oxide supports and provide insight into the reaction pathways responsible for their enhanced deoxygenation performance.

Bifunctional Catalysts for Upgrading of Biomass-Derived Oxygenates: A Review

“…This synergistic effect was particularly important at elevated temperatures (623 K). 71 There has also been some interest in using zeolites as the solid acid component of these bifunctional systems. While their low activity towards phenolic reforming and high rates of coke generation make zeolites potentially less attractive than the other upgrading catalysts highlighted here, these issues can be improved by adding metals to the zeolite.…”

“…For example, m-cresol was shown to preferentially follow the ring hydrogenation route to deoxygenation over pure group VIII metals such as Ni, Pd, and Pt (shown by the saturated compounds in Figure 5). 34,71 However, when an oxophilic modifier was added to the catalyst a tautomerization pathway became accessible, creating a keto intermediate which may then be dehydrated to form toluene. By making this additional deoxygenation pathway energetically favorable the deoxygenation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 activity is increased.…”

Controlled deposition of titanium oxide overcoats by non-hydrolytic sol gel for improved catalyst selectivity and stability

“…We investigated the performances of our bifunctional platinum/ acid sites in the hydrodeoxygenation of oxygenated aromatics derived from the lignin fraction of biomass [72][73][74][75][76][77][78][79][80][81][82][83]. of acid sites close to metal nanoparticles has been shown to favor CAO bond cleavage and therefore deoxygenation.…”

Experimental and First‐Principles Evidence for Interfacial Activity of Ru/TiO2 for the Direct Conversion of m‐Cresol to Toluene

“…On the basis of density functional theory (DFT) simulations it was proposed that this observation can be explained by a water‐assisted direct C−O cleavage mechanism across the Ru/TiO 2 interface and the amphoteric character of TiO 2 , i.e., its ability to accept and donate protons . Similar enhancements in the rate of aromatics formation have been observed in the literature for other metal/oxide systems such as Pt/TiO 2 , and Pd/ZrO 2 and the improvement was attributed to support reducibility or oxophilicity ,. In addition to the choice of metal/oxide support, the nature of the reactant influences the location of the active site.…”