The size and morphology of the active phase (metal or metal oxide) are critical for the performance of heterogeneous catalysts. Conventional approaches for catalyst synthesis involve the modi cation of pore size and structure, the use of ligands to anchor the metal during preparation or the use of nanostructured oxides with well-de ned facets to provide suitable sites for metal nucleation and growth. However, these approaches may not yield durable catalysts for high temperature applications, such as the treatment of unburnt methane from natural gas fueled engines. Here we demonstrate an approach that relies on the trapping of metal single atoms on the support surface, in thermally stable form, to modify the nature of deposited metal/metal oxide clusters. By anchoring Pt ions on the catalyst support we can tailor the morphology of the deposited phase. In particular, two-dimensional (2-D) rafts of Pt/PtO x on the engineered catalyst support are formed by this approach, as opposed to three-dimensional (3-D) metal oxide nanoparticles on conventional supports. Adopting this approach for the synthesis of bimetallic catalysts via addition of Pd to the atom-trapped catalyst support (Pt@CeO 2 ) we found that the resulting Pd/Pt@CeO 2 catalyst provides improved thermal stability and water tolerance during methane oxidation.We attribute the improved performance to the 2-D morphology of the Pd/PdO phase present on the atomtrapped catalyst support. The results show that modifying the support by trapping single atoms could provide an important addition to the toolkit of catalyst designers to engineer catalyst supports for controlling the nucleation and growth of metal and metal oxide clusters in heterogeneous catalysts. the metal salt precursor on an oxide support 1 , via the methods of deposition-precipitation or strong electrostatic adsorption (SEA) 2 . Using these approaches, it is possible to achieve atomic dispersion of the deposited metal on a number of catalyst supports [3][4][5][6] . The interaction between the metal salt precursor and the functional groups on the surface (hydroxyls) determines the surface concentration of the dispersed phase. The nature and morphology of the dispersed phase depends on the surface structure of the oxide support 7, 8 , which can be manipulated by using faceted oxides as supports, or by introducing ligands on the support 9 . By pre-calcining the support, the number of hydroxyls on the support can be changed, which allows some control over the metal deposition (Scheme 1a).However, once the catalyst is treated at high temperatures, the mobility of the deposited metal leads to formation of thermodynamically stable structures, where the in uence of the initial preparation steps is lost. Here we explore an alternate approach where we trap metal atoms on the support to modify the

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First principles periodic density functional theory (DFT) calculations, in conjunction with detailed microkinetic modeling and experimental characterization, are employed to elucidate the structure sensitivity and identify key selectivity descriptors for nonoxidative propane dehydrogenation (PDH) on intermetallic alloys. A comprehensive theoretical treatment of 1:1 PdIn surfaces demonstrates that the Pd-terminated steps have 5 orders of magnitude higher rates than do the (110) terraces, with nearly complete selectivity to propylene formation. Pure Pd steps and terraces, in contrast, have considerably lower propylene selectivity and higher coverages of adsorbed intermediates, suggesting that Pd may experience more coking and reduced lifetimes compared to the alloys. A degree of rate and selectivity control analysis on the optimized microkinetic model demonstrates that propane C–H bond scission to yield 1-propyl is the most kinetically relevant step for propylene formation, while the C–C bond breaking barriers are important for byproduct formation. From these analyses, a simplified rate expression is derived for the step surface of the alloy, leading to the identification of a selectivity descriptor expressed in terms of effective free energy barriers of the rate controlling transition states, propane C–H bond breaking, and propyne C–C bond breaking. This descriptor is subsequently generalized to evaluate the propylene production selectivities for a series of Pd-containing alloys. The results show enhanced agreement with experimentally measured selectivity trends compared to traditional selectivity descriptors, suggesting a general strategy for identification of highly selective, nonoxidative PDH alloy catalysts.

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Nongeminate charge recombination occurs over a broad range of time scales in polymer solar cells and represents a serious loss channel for the performance and lifetime of devices. Multiple factors influence this process, including changes in morphology and formation of permanent defects, but individual contributions are often difficult to resolve from conventional experiments. We use intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) to investigate nongeminate charge recombination in blends of poly[2,6-(4,4-bis-(2-ethylhexyl)-4 H-cyclopenta [2,1- b;3,4- b']dithiophene)- alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) and [6,6]-phenyl-C-butyric acid methyl ester (PCBM) solar cells. PCPDTBT/PCBM devices are exposed to varying doses of UV light resonant with PCBM to induce small perturbations in the thin film morphology, namely local heating. IMPS/IMVS sweeps display signatures unique to degradation, that is, photocurrent and photovoltage leading the excitation light modulation appearing as positive phase shifts or 1st quadrant features in Bode and Nyquist representations, respectively. We assign this component to interface charging at purified PCPDTBT/PCBM phase boundaries that trap mobile charges and facilitate nongeminate recombination. Time- and frequency-domain drift-diffusion simulations are then used to model the perturbed photocurrent responses that show good agreement with experiments. Trap occupancies and their impact of photocurrent production are investigated using variable background (dc) excitation light intensities revealing increases of the 1st quadrant component in devices irradiated for longer times. No evidence of chemical degradation was observed from molecular spectroscopy and imaging experiments, and we conclude that morphological changes are chiefly responsible for larger nongeminate charge recombination yields as devices age. Lastly, we propose that the 1st quadrant IMPS/IMVS is a universal signature of morphology-related degradation, although its relative contribution may vary between material systems.