Trends in the Activation of Light Alkanes on Transition-Metal Surfaces

Abstract

The first (oxidative) dehydrogenation step of light alkanes (ethane, propane, and n-butane) on transition-metal (closed-packed and stepped) surfaces is analyzed using density functional theory (DFT) calculations. It is shown that the transition-state energies (ΔE TS) of the C–H bond activation scale linearly with the corresponding final-state energies (ΔE FS), and all alkanes studied here share the same linear scaling relationships for the nonoxidative, oxygen-assisted, and hydroxyl-assisted reactions. Variations in ΔE TS between alkanes can be mainly attributed to differences in dispersion contributions determined by the carbon-chain length. As the carbon chain increases, the ΔE TS of the alkane C–H bond activation decreases. In addition, the ΔE TS of the first (O)­DH step of propane and n-butane is linearly correlated with the ΔE TS of the first ethane (O)­DH step. We also find that the oxygen and hydroxyl adsorption energies on the transition-metal surfaces (closed-packed and stepped) are dictating the promoting/poisoning effect of the C–H bond activation. Based on our extensive DFT calculations, we find that Pt has the lowest C–H bond transition-state energy for both the nonoxidative and oxidative pathways, and metals such as Au and Ag become active for C–H bond activation of alkanes only when oxygen and hydroxyl species are present on the metal surfaces. Finally, by establishing scaling relationships over a wide range of transition-metal surfaces, we have developed a simple and highly accurate model for the prediction of C–H bond activation barriers for the (oxidative) dehydrogenation of light alkanes.

Selective Hydrogenation of Crotonaldehyde on SiO2‐Supported Pt Clusters: A DFT Study

“…Conversely, density functional theory (DFT) is a powerful tool that can be used to investigate a detailed chemical reaction at the microscopic level. [13][14][15] To clarify the hydrogenation mechanism of CAL on Pt, Hu et al used a microkinetic model to investigate the reaction mechanism on flat Pt (111). [16,17] This pioneering work undoubtedly deepen our understanding on hydrogenation of 𝛼,𝛽-unsaturated aldehydes, especially on the 1,4-addition hydrogenation mechanism.…”

“…Conversely, density functional theory (DFT) is a powerful tool that can be used to investigate a detailed chemical reaction at the microscopic level. [ 13–15 ] To clarify the hydrogenation mechanism of CAL on Pt, Hu et al. used a microkinetic model to investigate the reaction mechanism on flat Pt (111).…”

Automated Generation of Microkinetics for Heterogeneously Catalyzed Reactions Considering Correlated Uncertainties**

“…Thus, all correlated changes in the enthalpy of formation of the intermediates are propagated to the activation barrier. Since BEP relations are only approximate, we added a quasi‐random uncertainty via Sobol sequences to the intercept and slope of the BEP, [16] estimated from BEEF‐vdW calculations [42] (see Figure S6).…”

Automated Generation of Microkinetics for Heterogeneously Catalyzed Reactions Considering Correlated Uncertainties

“…Thus, all correlated changes in the enthalpy of formation of the intermediates are propagated to the activation barrier. Since BEP relations are only approximate, we added a quasi-random uncertainty via Sobol sequences to the intercept and slope of the BEP [17] , estimated from BEEF-vdW calculations [40] (see Figure S5).…”