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1. Circumventing the scaling relationship on bimetallic monolayer electrocatalysts for selective CO ₂ reduction

   https://doi.org/10.1039/d2sc00135g  

   Zhao, Zhonglong; Lu, Gang (March 2022, Chemical Science)

   Electrochemical conversion of CO 2 into value-added chemicals continues to draw interest in renewable energy applications. Although many metal catalysts are active in the CO 2 reduction reaction (CO 2 RR), their reactivity and selectivity are nonetheless hindered by the competing hydrogen evolution reaction (HER). The competition of the HER and CO 2 RR stems from the energy scaling relationship between their reaction intermediates. Herein, we predict that bimetallic monolayer electrocatalysts (BMEs) – a monolayer of transition metals on top of extended metal substrates – could produce dual-functional active sites that circumvent the scaling relationship between the adsorption energies of HER and CO 2 RR intermediates. The antibonding interaction between the adsorbed H and the metal substrate is revealed to be responsible for circumventing the scaling relationship. Based on extensive density functional theory (DFT) calculations, we identify 11 BMEs which are highly active and selective toward the formation of formic acid with a much suppressed HER. The H–substrate antibonding interaction also leads to superior CO 2 RR performance on monolayer-coated penta-twinned nanowires. 

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2. Insights into how the aqueous environment influences the kinetics and mechanisms of heterogeneously-catalyzed COH* and CH ₃ OH* dehydrogenation reactions on Pt(111)

   https://doi.org/10.1039/C9CP00824A  

   Bodenschatz, Cameron J.; Xie, Tianjun; Zhang, Xiaohong; Getman, Rachel B. (May 2019, Physical Chemistry Chemical Physics)

   Water influences catalytic reactions in multiple ways, including energetic and mechanistic effects. While simulations have provided significant insight into the roles that H 2 O molecules play in aqueous-phase heterogeneous catalysis, questions still remain as to the extent to which H 2 O structures influence catalytic mechanisms. Specifically, influences of the configurational variability in the water structures at the catalyst interface are yet to be understood. Configurational variability is challenging to capture, as it requires multiscale approaches. Herein, we apply a multiscale sampling approach to calculate reaction thermodynamics and kinetics for COH* dehydrogenation to CO* and CH 3 OH* dehydrogenation to CH 2 OH* on Pt(111) catalysts under liquid H 2 O. We explore various pathways for these dehydrogenation reactions that could influence the overall mechanism of methanol decomposition by including participation of H 2 O structures both energetically and mechanistically. We find that the liquid H 2 O environment significantly influences the mechanism of COH* dehydrogenation to CO* but leaves the mechanism of CH 3 OH* dehydrogenation to CH 2 OH* largely unaltered. 

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3. Controlling product selectivity in hybrid gas/liquid reactors using gas conditions, voltage, and temperature

   https://doi.org/10.1039/D3NR00561E  

   Lee, Seung-Hoon; Iglesias, Brandon; Everitt, Henry O.; Liu, Jie (June 2023, Nanoscale)

   For the conversion of CO 2 into fuels and chemical feedstocks, hybrid gas/liquid-fed electrochemical flow reactors provide advantages in selectivity and production rates over traditional liquid phase reactors. However, fundamental questions remain about how to optimize conditions to produce desired products. Using an alkaline electrolyte to suppress hydrogen formation and a gas diffusion electrode catalyst composed of copper nanoparticles on carbon nanospikes, we investigate how hydrocarbon product selectivity in the CO 2 reduction reaction in hybrid reactors depends on three experimentally controllable parameters: (1) supply of dry or humidified CO 2 gas, (2) applied potential, and (3) electrolyte temperature. Changing from dry to humidified CO 2 dramatically alters product selectivity from C 2 products ethanol and acetic acid to ethylene and C 1 products formic acid and methane. Water vapor evidently influences product selectivity of reactions that occur on the gas-facing side of the catalyst by adding a source of protons that alters reaction pathways and intermediates. 

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4. Bimetallenes for selective electrocatalytic conversion of CO ₂ : a first-principles study

   https://doi.org/10.1039/d0ta03099f  

   Zhao, Zhonglong; Lu, Gang (June 2020, Journal of Materials Chemistry A)

   null (Ed.)

   Two-dimensional (2D) materials are full of surprises and fascinating potential. Motivated by a recent discovery that sub-nanometer PdMo bimetallenes can realize exceptional performance in the oxygen reduction reaction [ Nature 2019, 574 , 81–85], we explore the potential of 2D bimetallenes for catalyzing the CO 2 electroreduction reaction (CO 2 RR). Following extensive first-principles calculations on more than a hundred bimetallenes, we identify 17 Cu- and Ag-based bimetallenes, which are highly active and selective toward the formation of formic acid and simultaneously suppress the competing hydrogen evolution reaction. Equally important, we find that CO 2 RR products via intermediates of COOH and CO are disfavored on these bimetallenes. Although surface strains are developed on the bimetallenes, their contribution to the catalytic activities is moderate as compared to that of the alloying effect. This work opens the door to future applications of bimetallenes as active and selective catalysts for the CO 2 RR. 

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5. Improving alkane dehydrogenation activity on γ-Al ₂ O ₃ through Ga doping

   https://doi.org/10.1039/d0cy01474e  

   Abdelgaid, Mona; Dean, James; Mpourmpakis, Giannis (November 2020, Catalysis Science & Technology)

   null (Ed.)

   Nonoxidative alkane dehydrogenation is a promising route to produce olefins, commonly used as building blocks in the chemical industry. Metal oxides, including γ-Al 2 O 3 and β-Ga 2 O 3 , are attractive dehydrogenation catalysts due to their surface Lewis acid–base properties. In this work, we use density functional theory (DFT) to investigate nonoxidative dehydrogenation of ethane, propane, and isobutane on the Ga-doped and undoped (100) γ-Al 2 O 3 via the concerted and stepwise mechanisms. We revealed that doping (100) γ-Al 2 O 3 with Ga atoms has significant improvement in the dehydrogenation activity by decreasing the C–H activation barriers of the kinetically favored concerted mechanism and increasing the overall dehydrogenation turnover frequencies. We identified the dissociated H 2 binding energy as an activity descriptor for alkane dehydrogenation, accounting for the strength of the Lewis acidity and basicity of the active sites. We demonstrate linear correlations between the dissociated H 2 binding energy and the activation barriers of the rate determining steps for both the concerted and stepwise mechanisms. We further found the carbenium ion stability to be a quantitative reactant-type descriptor, correlating with the C–H activation barriers of the different alkanes. Importantly, we developed an alkane dehydrogenation model that captures the effect of catalyst acid–base surface properties (through dissociated H 2 binding energy) and reactant substitution (through carbenium ion stability). Additionally, we show that the dissociated H 2 binding energy can be used to predict the overall dehydrogenation turnover frequencies. Taken together, our developed methodology facilitates the screening and discovery of alkane dehydrogenation catalysts and demonstrates doping as an effective route to enhance catalytic activity. 

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