The complexity of heterogeneous catalysts means that a priori design of new catalytic materials is difficult, but the well-defined nature of single-atom–alloy catalysts has made it feasible to perform unambiguous theoretical modeling and precise surface science experiments. Herein we report the theory-led discovery of a rhodium-copper (RhCu) single-atom–alloy catalyst for propane dehydrogenation to propene. Although Rh is not generally considered for alkane dehydrogenation, first-principles calculations revealed that Rh atoms disperse in Cu and exhibit low carbon-hydrogen bond activation barriers. Surface science experiments confirmed these predictions, and together these results informed the design of a highly active, selective, and coke-resistant RhCu nanoparticle catalyst that enables low-temperature nonoxidative propane dehydrogenation.

Acid and redox reaction rates of CH 3 OH-O 2 mixtures on polyoxometalate (POM) clusters, together with isotopic, spectroscopic, and theoretical assessments of catalyst properties and reaction pathways, were used to define rigorous descriptors of reactivity and to probe the compositional effects for oxidative dehydrogenation (ODH) and dehydration reactions. 31 P-MAS NMR, transmission electron microscopy and titrations of protons with di-tert-butylpyridine during catalysis showed that POM clusters retained their Keggin structure upon dispersion on SiO 2 and after use in CH 3 OH reactions. The effects of CH 3 OH and O 2 pressures and of Dsubstitution on ODH rates show that C−H activation in molecularly adsorbed CH 3 OH is the sole kinetically relevant step and leads to reduced centers as intermediates present at low coverages; their concentrations, measured from UV−vis spectra obtained during catalysis, are consistent with the effects of CH 3 OH/O 2 ratios predicted from the elementary steps proposed. First-order ODH rate constants depend strongly on the addenda atoms (Mo vs W) but weakly on the central atom (P vs Si) in POM clusters, because C−H activation steps inject electrons into the lowest unoccupied molecular orbitals (LUMO) of the clusters, which are the d-orbitals at Mo 6+ and W 6+ centers. H-atom addition energies (HAE) at O-atoms in POM clusters represent the relevant theoretical probe of the LUMO energies and of ODH reactivity. The calculated energies of ODH transition states at each O-atom depend linearly on their HAE values with slopes near unity, as predicted for late transition states in which electron transfer and C−H cleavage are essentially complete. HAE values averaged over all accessible O-atoms in POM clusters provide the appropriate reactivity descriptor for oxides whose known structures allow accurate HAE calculations. CH 3 OH dehydration proceeds via parallel pathways mediated by late carbenium-ion transition states; effects of composition on dehydration reactivity reflect changes in charge reorganizations and electrostatic forces that stabilize protons at Brønsted acid sites.

S1. Comparison of broken-symmetry transition state energies with their single point energies derived from triplet and closed-shell singlet calculationsAs described in Section 3.3 of the main text and elsewhere in the literature, S1-S3 the C-H bond activation in organic molecules can lead to formation of radical-like species that are more stable in their triplet electronic state than singlet. The greater stability of the triplet states leads to crossing of the singlet and triplet potential energy surfaces along the reaction coordinate for C-H activation, which leads to broke-symmetry C-H activation transition states near the crossing points. The examples of the activation of C-H bonds shown in bold in CH 4 , CH 3 OH and (CH 3 ) 2 CHOH in the main text (Figs. 3-4, main text) the singlet-triplet energy difference for the radials after C-H activation decreases with decreasing C-H bond strength, and when C-H bonds become sufficiently weak, the spin-crossing after C-H activation is completely avoided and all transition states exist as closed-shell singlets. Here, we show such trends for a broader set of C-H

Density functional theory (DFT) calculations of energetic, geometric, vibrational, and electrostatic properties of different arrangements of CO and NO at quarter and half monolayer coverage on Pt(111) are presented. Differences in the extents of electron back-donation from the Pt surface to these molecules cause the low-coverage adsorbate dipoles to have opposite signs at atop and more highly coordinated bridge or fcc sites. These dipoles of opposite sign occupy adjacent positions in the experimentally observed atop-bridge or atop-fcc high -coverage arrangements, leading to attractive electrostatic interactions and concomitant changes in dipole moments, bond lengths, and vibrational frequencies. The interaction energies are estimated by charge partitioning to extract individual dipoles from the mixed arrangement and by calculations of field-dipole interactions. These estimated dipole interactions contribute significantly (20-60%) to the DFT-calculated relative stability of mixed arrangements over atop-, bridge-, or fcc-only arrangements and thus play an important role in coverage-dependent adsorption. We further extend these analyses to a range of molecules with varying dipole moments and show that the general nature of these interactions is not limited to CO and NO.

M1 phase MoVTeNb mixed oxides exhibit unique catalytic properties that lead to high C2H4 yields in oxidative conversion of C2H6 at moderate temperatures. The role of the heptagonal channel micropores of the M1 phase in regulating reactivity and selectivity is assessed here using reactant size-dependent kinetic probes and density functional theory (DFT) treatments for C2H6 and cyclohexane (C6H12) activations inside and outside the micropores. The sizes of C2H6 and the micropores suggest a tight guest–host fit, but C6H12 cannot access intrapore sites. Measured C2H6 to C6H12 activation rate ratios on MoVTeNbO are much higher than those measured on nonmicroporous vanadium oxides (VO x /SiO2) and estimated by DFT on external surfaces, suggesting that most C2H6 activations on MoVTeNbO occur inside the micropores under typical conditions. C2H6 exhibits higher activation energy than C6H12 on VO x /SiO2, consistent with the corresponding C–H bond strengths; the activation energy difference between C2H6 and C6H12 is lower on MoVTeNbO because micropores stabilize C–H activation transition states through van der Waals interactions. Product selectivities for C2H6 and C6H12 suggest that the ability of VO x /SiO2 to activate C–H bonds and resist O-insertion in products is similar to the external surfaces of MoVTeNbO, but the micropores in the latter oxides are more selective for C–H activation. DFT calculations show that the tight confinement in micropores hinders the C–O contact necessary for O-insertion. These insights provide guidance for utilizing shapes and sizes of confining voids to mitigate selectivity limitations dictated by thermodynamics of sequential oxidation reactions and electronic properties of redox catalysts.