Near-Surface Gas-Phase Methoxymethanol Is Generated by Methanol Oxidation over Pd-Based Catalysts

Advances and Challenges in Speciation Measurement and Microkinetic Modeling for Gas-Solid Heterogeneous Catalysis

Microkinetic modeling of heterogeneous catalysis serves as an efficient tool bridging atom-scale first-principles calculations and macroscale industrial reactor simulations. Fundamental understanding of the microkinetic mechanism relies on a combination of experimental and theoretical studies. This Perspective presents an overview of the latest progress of experimental and microkinetic modeling approaches applied to gas-solid catalytic kinetics. Then, opportunities and challenges are presented based on recent research progress in gas-solid catalysis and combustion chemistry. For experimental approaches, the importance of ideal catalytic reactors, structured catalysts, and precise elementary rate measurements is emphasized. Additionally, integrating spatiotemporally resolved operando gas-phase diagnostics with surface-adsorbed species characterization methods offers new opportunities for gaining deeper insights into gas-surface reactions. In microkinetic modeling, a hybrid rate parameter evaluation approach that combines first-principles calculations with semiempirical methods, followed by automated mechanism generation and data-driven optimization, opens new avenues for efficiently constructing surface mechanisms. Furthermore, extending microkinetic modeling beyond mean-field approximations allows simulations under realistic catalyst operating conditions. Finally, the critical role of gas-phase mechanisms and comprehensive microkinetic modeling analyses in advancing our fundamental understanding of gas-solid catalytic processes is highlighted.

The Far-Infrared Spectrum of Methoxymethanol (CH3-O-CH2OH): A Theoretical Study

Methoxymethanol (CH3OCH2OH), an oxygenated volatile organic compound of low stability detected in the interstellar medium, represents an example of nonrigid organic molecules showing various interacting and inseparable large-amplitude motions. The species discloses a relevant coupling among torsional modes, strong enough to prevent complete assignments using effective Hamiltonians of reduced dimensionality. Theoretical models for rotational spectroscopy can improve if they treat three vibrational coordinates together. In this paper, the nonrigid properties and the far-infrared region are analyzed using highly correlated ab initio methods and a three-dimensional vibrational model. The molecule displays two gauche-gauche (CGcg and CGcg') and one trans-gauche (Tcg) conformers, whose relative energies are very small (CGcg/CGcg'/Tcg = 0.0:641.5:792.7 cm-1). The minima are separated by relatively low barriers (1200-1500 cm-1), and the corresponding methyl torsional barriers V 3 are estimated to be 595.7, 829.0, and 683.7 cm-1, respectively. The ground vibrational state rotational constants of the most stable geometry have been computed to be A 0 = 17233.99 MHz, B 0 = 5572.58 MHz, and C 0 = 4815.55 MHz, at ΔA 0 = -3.96 MHz, ΔB 0 = 4.76 MHz, and ΔC 0 = 2.51 MHz from previous experimental data. Low-energy levels and their tunneling splittings are determined variationally up to 700 cm-1. The A/E splitting of the ground vibrational state was computed to be 0.003 cm-1, as was expected given the methyl torsional barrier (∼600 cm-1). The fundamental levels (100), (010), and (001) are predicted at 132.133 and 132.086 cm-1 (methyl torsion), 186.507 and 186.467 cm-1 (O-CH3 torsion), and 371.925 and 371.950 cm-1 (OH torsion), respectively.

The photoionization of methoxymethanol: Fingerprinting a reactive C2 oxygenate in a complex reactive mixture

Methoxymethanol (CH3OCH2OH) is a reactive C2 ether-alcohol that is formed by coupling events in both heterogeneous and homogeneous systems. It is found in complex reactive environments-for example those associated with catalytic reactors, combustion systems, and liquid-phase mixtures of oxygenates. Using tunable synchrotron-generated vacuum-ultraviolet photons between 10.0 and 11.5 eV, we report on the photoionization spectroscopy of methoxymethanol. We determine that the lowest-energy photoionization process is the dissociative ionization of methoxymethanol via H-atom loss to produce [C2H5O2]+, a fragment cation with a mass-to-charge ratio (m/z) = 61.029. We measure the appearance energy of this fragment ion to be 10.24 ± 0.05 eV. The parent cation is not detected in the energy range examined. To elucidate the origin of the m/z = 61.029 (C2H5O2) fragment, we used automated electronic structure calculations to identify key stationary points on the cation potential energy surface and compute conformer-specific microcanonical rate coefficients for the important unimolecular processes. The calculated H-atom dissociation pathway results in a [C2H5O2]+ fragment appearance at 10.21 eV, in excellent agreement with experimental results.