Energetics of Adsorbed Methyl and Methyl Iodide on Ni(111) by Calorimetry: Comparison to Pt(111) and Implications for Catalysis

Importance sampling within configuration space integration for adsorbate thermophysical properties: a case study for CH3/Ni(111)

A new strategy is presented for computing anharmonic partition functions for the motion of adsorbates relative to a catalytic surface. Importance sampling is compared with conventional Monte Carlo. The importance sampling is significantly more efficient. This new approach is applied to CH3* on Ni(111) as a test case. The motion of methyl relative to the nickel surface is found to be anharmonic, with significantly higher entropy compared to the standard harmonic oscillator model. The new method is freely available as part of the Minima-Preserving Neural Network within the ADTHERM package.

DFT benchmark studies on representative species and poisons of methane steam reforming on Ni(111)

Ni catalysts used in methane steam reforming (MSR) are highly susceptible to poisoning by carbon-based species, which poses a major impediment to the productivity of industrial operations. These species encompass graphitic carbon-like formations that are typically modelled as graphene. First principles-based approaches, such as density functional theory (DFT) calculations, can provide valuable insight into the mechanism of graphene growth in the MSR reaction. It is, however, critical that a DFT model of this reaction can accurately describe the interactions of Ni(111) with the MSR intermediates as well as graphene. In this work, a systematic benchmark study has been carried out to identify a suitable DFT functional for the graphene-MSR system. The binding energies of graphene and important MSR species, as well as the reaction energies of methane dissociation and carbon oxidation, were computed on Ni(111) using GGA functionals, DFT-D and van der Waals density functionals (vdW-DF). It is well-established that the GGA functionals are inadequate for describing graphene-Ni(111) interactions. In the case of vdW-DF, the optPBE-vdW functional predicts the binding energies of graphene and several important MSR species with reasonable accuracy; however, it provides poor estimates of CO and O binding energies. Among the DFT-D functionals, PBE-D3 and PBE-dDsC have been found to exhibit acceptable accuracy for graphene and most MSR species (excluding adsorbed CO), and therefore, both functionals are promising for elucidating carbon-based catalytic poisoning in the MSR reaction. Overall, no single DFT functional could estimate the binding energies of all the species with equally high accuracy.

Energies of Adsorbed Catalytic Intermediates on Transition Metal Surfaces: Calorimetric Measurements and Benchmarks for Theory

Better catalysts and electrocatalysts are essential for the production and use of clean fuels with less pollution and improved energy efficiency, for making chemicals with less energy and environmental impact, for pollution abatement, and for many other future technologies needed to achieve environmentally friendlier energy supply and chemicals industry. Crucial for rational design of better catalyst and electrocatalyst materials is knowledge of the energies of elementary chemical reactions on late transition metal surfaces. This knowledge would also aid in designing more efficient and stable photocatalysts and batteries for harvesting and storing solar energy. These are all crucial for sustainable living with high quality. Herein, I review measurements of surface reaction energies involving many of the most common adsorbates formed as intermediates on late transition metal surfaces in catalytic and electrocatalytic reactions of interest for energy and environmental technologies. I focus on calorimetric measurements of the heat of molecular and dissociative adsorption of gases on single crystals (i.e., single crystal adsorption calorimetry, or SCAC) that allow the heats of formation of adsorbed intermediates in well-defined structures to be directly determined. Adsorption reactions are often irreversible, and in such cases SCAC is required to get these heats, since the other methods for measuring adsorption energies (equilibrium adsorption isotherms and temperature-programmed desorption) work only for reversible adsorption. Common examples of irreversible adsorption reactions are ones that produce adsorbed molecular fragments or adsorbed molecules such as olefins and aromatic molecules that bind very strongly to non-noble metals. When the heats of formation of different adsorbed molecular fragments are compared to each other, and to their values on different metal surfaces, they reveal which properties of the metal surface and the molecular fragments determine metal-adsorbate bond strengths, and clarify differences in catalytic reactivity between different metals. When combined with earlier adsorption energy measurements, these heats also provide a database of reliable energies of adsorbed catalytic intermediates that serve as crucial benchmarks to guide the development of improved computational methods for calculating the energetics of elementary steps on late transition metal surfaces (i.e., reaction energies and activation barriers), such as density functional theory. The energy accuracy of such computational estimates is crucial for the future of catalysis research and catalyst discovery.