4 research outputs found

    Understanding the Optimal Adsorption Energies for Catalyst Screening in Heterogeneous Catalysis

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    The fundamental understanding of the activity in heterogeneous catalysis has long been the major subject in chemistry. This paper shows the development of a two-step model to understand this activity. Using the theory of chemical potential kinetics with Brønsted–Evans–Polanyi relations, the general adsorption energy window is determined from volcano curves, using which the best catalysts can be searched. Significant insights into the reasons for catalytic activity are obtained

    Mechanistic Study of 1,3-Butadiene Formation in Acetylene Hydrogenation over the Pd-Based Catalysts Using Density Functional Calculations

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    Green oil, which leads to the deactivation of the catalysts used for the selective hydrogenation of acetylene, has long been observed but its formation mechanism is not fully understood. In this work, the formation of 1,3-butadiene, known to be the precursor of green oil, on both Pd(111) and Pd(211) surfaces is examined using density functional theory calculations. The pathways containing C<sub>2</sub> + C<sub>2</sub> coupling reactions as well as the corresponding hydrogenation reactions are studied in detail. Three pathways for 1,3-butadiene production, namely coupling plus hydrogenation and further hydrogenation, hydrogenation plus coupling plus hydrogenation, and a two step hydrogenation followed by coupling, are determined. By comparing the effective barriers, we identify the favored pathway on both surfaces. A general understanding toward the deactivation process of the industrial catalysts is also provided. In addition, the effects of the formation of subsurface carbon atoms as well as the Ag alloying on the 1,3-butadiene formation on Pd-based catalysts are also investigated and compared with experimental results

    Origin of the Increase of Activity and Selectivity of Nickel Doped by Au, Ag, and Cu for Acetylene Hydrogenation

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    Activity and selectivity are both important issues in heterogeneous catalysis and recent experimental results have shown that Ni catalysts doped by gold exhibit high activity for the hydrogenation of acetylene with good selectivity of ethylene formation. To unravel the underlying mechanism for this observation, the general trend of activity and selectivity of Ni surfaces doped by Au, Ag, and Cu has been investigated using density functional theory calculations. Complete energy profiles from C<sub>2</sub>H<sub>2</sub> to C<sub>2</sub>H<sub>4</sub> on Ni(111), Au/Ni(111), Ag/Ni(111) and Cu/Ni(111) are obtained and their turnover frequencies (TOFs) are computed. The results show that acetylene adsorption on Ni catalyst is strong which leads to the low activity while the doping of Au, Ag, and Cu on the Ni catalyst weakens the acetylene adsorption, giving rise to the increase of activity. The selectivity of ethylene formation is also quantified by using the energy difference between the hydrogenation barriers and the absolute value of the adsorption energies of ethylene. It is found that the selectivity of ethylene formation increases by doping Au and Ag, while those of Cu/Ni and Ni are similar

    Ambient Temperature Hydrocarbon Selective Catalytic Reduction of NO<sub><i>x</i></sub> Using Atmospheric Pressure Nonthermal Plasma Activation of a Ag/Al<sub>2</sub>O<sub>3</sub> Catalyst

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    Atmospheric pressure nonthermal-plasma-activated catalysis for the removal of NO<sub><i>x</i></sub> using hydrocarbon selective catalytic reduction has been studied utilizing toluene and <i>n</i>-octane as the hydrocarbon reductant. When the plasma was combined with a Ag/Al<sub>2</sub>O<sub>3</sub> catalyst, a strong enhancement in activity was observed when compared with conventional thermal activation with high conversions of both NO<sub><i>x</i></sub> and hydrocarbons obtained at temperature ≤250 °C, where the silver catalyst is normally inactive. Importantly, even in the absence of an external heat source, significant activity was obtained. This low temperature activity provides the basis for applying nonthermal plasmas to activate emission control catalysts during cold start conditions, which remains an important issue for mobile and stationary applications
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