Ab Initio Surface Phase Diagrams for Coadsorption of Aromatics and Hydrogen on the Pt(111) Surface

Abstract

Supported metal catalysts are commonly used for the hydrogenation and deoxygenation of biomass-derived aromatic compounds in catalytic fast pyrolysis. To date, the substrate–adsorbate interactions under reaction conditions crucial to these processes remain poorly understood, yet understanding this is critical to constructing detailed mechanistic models of the reactions important to catalytic fast pyrolysis. Density functional theory (DFT) has been used in identifying mechanistic details, but many of these works assume surface models that are not representative of realistic conditions, for example, under which the surface is covered with some concentration of hydrogen and aromatic compounds. In this study, we investigate hydrogen-guaiacol coadsorption on Pt(111) using van der Waals-corrected DFT and ab initio thermodynamics over a range of temperatures and pressures relevant to bio-oil upgrading. We find that relative coverage of hydrogen and guaiacol is strongly dependent on the temperature and pressure of the system. Under conditions relevant to ex situ catalytic fast pyrolysis (CFP; 620–730 K, 1–10 bar), guaiacol and hydrogen chemisorb to the surface with a submonolayer hydrogen (∼0.44 ML H), while under conditions relevant to hydrotreating (470–580 K, 10–200 bar), the surface exhibits a full-monolayer hydrogen coverage with guaiacol physisorbed to the surface. These results correlate with experimentally observed selectivities, which show ring saturation to methoxycyclohexanol at hydrotreating conditions and deoxygenation to phenol at CFP-relevant conditions. Additionally, the vibrational energy of the adsorbates on the surface significantly contributes to surface energy at higher coverage. Ignoring this contribution results in not only quantitatively, but also qualitatively incorrect interpretation of coadsorption, shifting the phase boundaries by more than 200 K and ∼10–20 bar and predicting no guaiacol adsorption under CFP and hydrotreating conditions. The implications of this work are discussed in the context of modeling hydrogenation and deoxygenation reactions on Pt(111), and we find that only the models representative of equilibrium surface coverage can capture the hydrogenation kinetics correctly. Last, as a major outcome of this work, we introduce a freely available web-based tool, dubbed the Surface Phase Explorer (SPE), which allows researchers to conveniently determine surface composition for any one- or two-component system at thermodynamic equilibrium over a wide range of temperatures and pressures on any crystalline surface using standard DFT output.

Sustainable Routes for the Synthesis of Renewable Heteroatom-Containing Chemicals

“…The reason might be the heterogeneity and recalcitrance of lignin due to its extended C–C and C–O linking network or the change of the native lignin structure during the processing of lignocellulosic biomass under harsh conditions. Along this line, lignin was either actively stabilized before further treatment of the sugar components − or lignin was extracted from the biomass resource first. , Gaining a more fundamental understanding on the processes involved in biomass fractionation, − lignin depolymerization ,, and its partial or complete defunctionalization − may facilitate the development of more efficient catalyst, reactor and process designs. A certain emphasis has been put on the production of biorenewable polymers − because they are desirable products and are made from simple repeating units .…”

Coadsorption of Butadiene and Hydrogen on the (111) Surfaces of Pt and Pt2Sn Surface Alloy: Understanding the Cohabitation from First-Principles Calculations

“…Very recently, Fergusson et al studied the coadsorption of hydrogen and guaiacol on Pt(111) using a van der Waals-corrected DFT functional, and they showed that at conditions relevant to hydrotreatment the surface is covered by a monolayer of H atoms, while guaiacol is only physisorbed on top of this layer. 15 Besides catalytic activity, selectivity in targeted products is also crucial. Pt is a very active catalyst for the hydrogenation of unsaturated molecules; however, in the case of diolefins as butadiene, it leads to a mixture of partially hydrogenated butenes and totally hydrogenated butane.…”

Towardsoperandocomputational modeling in heterogeneous catalysis

“…The structures and stabilities of various nanoparticles used in catalysis were investigated as a function of synthesis conditions or “ operando ” environment, e.g. Mo 2 C, ZnO and Ni 2 P, 166 – 169 surface coverage as a function of T and p i , 161 , 170 – 172 doping effects, 173 metal alloying, 174 , 175 surfaces under electrochemical conditions, 176 , 177 water in the interlayer space, 178 or controlled growth conditions, 179 to name just some. Several recent reviews and perspectives are also available.…”