Accurately simulating heterogeneously catalyzed reactions requires reliable barriers for molecules reacting at defects on metal surfaces, such as steps. However, first-principles methods capable of computing these barriers to chemical accuracy have yet to be demonstrated. We show that state-resolved molecular beam experiments combined with ab initio molecular dynamics using specific reaction parameter density functional theory (SRP-DFT) can determine the molecule-metal surface interaction with the required reliability. Crucially, SRP-DFT exhibits transferability: the functional devised for methane reacting on a flat (111) face of Pt (and Ni) also describes its reaction on stepped Pt(211) with chemical accuracy. Our approach can help bridge the materials gap between fundamental surface science studies on regular surfaces and heterogeneous catalysis in which defected surfaces are important.

The dissociative chemisorption of small molecules such as methane and water on metal surfaces is a key step in many important catalyzed reactions. However, it has only very recently become possible to directly compare theory with molecular beam studies of these reactions. For most experimental conditions, such a comparison requires accurate methods for introducing the effects of lattice motion into quantum reactive scattering calculations. We examine these methods and their recent application to methane and water dissociative chemisorption. New results are presented for CO chemisorption and methane dissociation at step edges. The type of molecule-lattice coupling that leads to a strong variation in the dissociative sticking of methane with temperature is shown to occur for many polyatomic-metal systems. Improvements to these models are discussed. The ability to accurately compare theory with molecular beam experiments should lead to improved density functionals and consequently more accurate thermal rate constants for these important reactions.

, 2018 --Transition-metal catalysts, such as nickel and cobalt, are widely used in industry to produce hydrogen and other useful compounds from natural gas. Researchers achieve this transformation through steam reforming, which is the process of heating methane with steam in the presence of the catalyst, thus producing hydrogen and carbon monoxide.Transition metals are known for their superior catalytic capabilities and researchers know that the most significant reactions occur at the surface of the catalysts. So far, the search for even better catalysts has been largely based on trial and error, and on the assumption that catalyzed reactions take place on step edges and other atomic defect sites of the metal crystals.An international research team from Switzerland, the Netherlands, and the United States has combined experiments using advanced infrared techniques with quantum theory to explore methane dissociation reactions in minute detail. For the first time, their research shows exactly where the most significant reactions occur on the catalyst's surface. The researchers focused on platinum (Pt) as the catalyst to break down methane, but the model can be applied to other transition-metal catalysts, such as nickel. They report their findings this week in The Journal of Chemical Physics, from AIP Publishing."A tested predictive theory with chemical accuracy could change the way one searches for new catalysts and make the search more efficient and cheaper," said Rainer Beck, co-author of the paper and professor of chemical science and engineering at École Polytechnique Fédérale de Lausanne (EPFL).At the atomic scale, the surface of a platinum catalyst (as well as other metal crystals) can consist of steps, terraces, and other defects that are seen as important "sites" in the catalytic process.The Pt(211) surface has three-atom-wide terraces and one-atom-high steps. The researchers labeled the row of atoms on the step edge as "step" (red), the middle row as "terrace" (black) and the final row as "corner" (gray).

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The effect of Cr­(VI) and bisphenol A (BPA) on U­(VI) photoreduction by C3N4 photocatalyst was demonstrated by the batch experiments, electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) techniques. The batch experiments manifested that Cr­(VI) and BPA enhanced the photocatalytic activity of C3N4 for U­(VI) photoreduction, whereas U­(VI) photoreduction was significantly diminished with increased pH from 4.0 to 8.0. According to radical scavengers and ESR analysis, U­(VI) was photoreduced to U­(IV) by photogenerated electrons of conduction band edge, whereas Cr­(VI) was reduced to Cr­(III) by H2O2. BPA and its products such as organic acid and alcohols can capture photoinduced holes, which resulted in the enhancement of U­(VI) photoreduction to U­(IV). XPS and XANES analyses demonstrated that U­(VI) was gradually photoreduced to U­(IV) by C3N4 within irradiation 60 min, whereas U­(IV) was reoxidized to U­(VI) with increasing irradiation time. EXAFS analysis determined that the dominant interaction mechanisms of U­(VI) on C3N4 after irradiation for 240 min were reductive precipitation and inner-sphere surface complexation. This work highlights the synergistic removal of radionuclides, heavy metals, and persistent organic pollutants by C3N4, which is crucial for the design and application of a high-performance photocatalyst in actual environmental cleanup.