Propane dehydrogenation on a Pt-based catalyst can be accelerated by cofeeding hydrogen. An extensive reaction network for propane dehydrogenation on Pt(111), including side reactions and deep dehydrogenation reactions, is proposed to explain the effect of cofeeding hydrogen. Simulations at 873 K and 1 bar total pressure reproduce the experimental trends at increasing H2/C3H8 inlet ratios and allow exploration of the origin of the positive effect of cofeeding hydrogen. Increasing hydrogen pressure leads to a lower coverage of deeply dehydrogenated coke precursors on the surface: in particular, CCH3 (ethylidyne) and CH (methylidyne). In addition, it increases hydrogen coverage, which decreases the propylene adsorption strength while the energy barriers for the further dehydrogenation of propylene increase. The combined effect of a decreasing coke precursor coverage, facilitated propylene desorption, and increasing deep dehydrogenation barriers explains the higher catalytic activity when hydrogen is cofed.

The alloying of Pt with Ga delivered from a hydrotalcite-like support was investigated as a strategy to produce bimetallic catalysts for propane dehydrogenation. A series of Pt/Mg­(Al,Ga)­O x catalysts (2–3 wt % Pt, Ga/Pt molar ratios between 0 and 10) and a model Pt/Ga2O3 catalyst (4 wt % Pt, Ga/Pt molar ratio of 50) were characterized by means of X-ray diffraction (XRD), transmission electron microscopy, and activity measurements (873 K, W cat/F C3H8,0 = 25 kgcat·s·mol–1 and P C3H8,0 = 5 kPa at a total pressure of 101.3 kPa). XRD patterns taken during temperature-programmed reduction in 5% H2/He and isothermal reduction/oxidation cycling between 5% H2/He and 20% O2/N2 at 873 K revealed dynamic alloy formation and segregation that depended upon the gas environment and Ga content. Alloying on the Pt/Mg­(Al,Ga)­O x catalyst with a Ga/Pt ratio of 2 could not be observed by XRD. For a Ga/Pt ratio of 10, an alloy with a diffraction peak at 40.2° was formed during the initial reduction. After subsequent reduction/oxidation treatments, this catalyst evolved toward a stable periodic cycling between pure Pt and one or more Pt–Ga alloys with characteristic peaks at 40.2° and 46.5°. The exact composition of the Pt–Ga alloy(s) could not be identified. On the model Pt/Ga2O3 catalyst, an alloy was formed with the same characteristic peak at 40.2° as on the Ga-rich Pt/Mg­(Al,Ga)­O x . In addition, another Pt–Ga alloy appeared on the Pt/Ga2O3 catalyst, which was identified as a stoichiometric PtGa phase. These alloys were formed on Pt/Ga2O3 at a lower temperature than on Pt/Mg­(Al,Ga)­O x and they were stable during the reduction/oxidation cycling. Catalytic activity measurements demonstrated that the formation of Pt–Ga alloys on the Pt/Mg­(Al,Ga)­O x sample with a Ga/Pt ratio of 10 and on the Pt/Ga2O3 catalyst led to pronounced enhancement of the initial selectivity toward propylene, but lower activity per exposed Pt atom.

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Complementary to conventional X-ray absorption near edge structure (XANES) and Fourier transformed (FT) extended X-ray absorption fine structure (EXAFS) analysis, the systematic application of wavelet transformed (WT) XAS is shown to disclose the physicochemical mechanisms governing Pt-In catalyst formation. The simultaneous k- and R-space resolution of the WT XAS signal allows for the efficient allocation of the elemental nature to each R-space peak. Because of its elemental discrimination capacity, the technique delivers structural models which can subsequently serve as an input for quantitative FT EXAFS modeling. The advantages and limitations of applying WT XAS are demonstrated (1) before and (2) after calcination to 650 °C of a Pt(acac)2 impregnated Mg(In)(Al)Ox support and (3) after subsequent H2 reduction to 650 °C. Combined XANES, FT, and WT XAS analysis shows that the acac ligands of the Pt precursor decompose during calcination, leading to atomically dispersed Pt(4+) cations on the Mg(In)(Al)Ox support. H2 reduction treatment eventually results in the formation of 1.5 nm Pt-In alloyed nanoparticles. Widespread use and systematic application of wavelet-based XAS can potentially reveal in greater detail the intricate mechanisms involved in catalysis, chemistry, and related fields.

Hydrogen plays an essential role during the in situ assembly of tailored catalytic materials, and serves as key ingredient in multifarious chemical reactions promoted by these catalysts. Despite intensive debate for several decades, the existence and nature of hydrogen-involved mechanisms - such as hydrogen-spillover, surface migration - have not been unambiguously proven and elucidated up to date. Here, Pt-Ga alloy formation is used as a probe reaction to study the behavior and atomic transport of H and Ga, starting from Pt nanoparticles on hydrotalcite-derived Mg(Ga)(Al)Ox supports. In situ XANES spectroscopy, time-resolved TAP kinetic experiments, HAADF-STEM imaging and EDX mapping are combined to probe Pt, Ga and H in a series of H2 reduction experiments up to 650 °C. Mg(Ga)(Al)Ox by itself dissociates hydrogen, but these dissociated hydrogen species do not induce significant reduction of Ga(3+) cations in the support. Only in the presence of Pt, partial reduction of Ga(3+) into Ga(δ+) is observed, suggesting that different reaction mechanisms dominate for Pt- and Mg(Ga)(Al)Ox-dissociated hydrogen species. This partial reduction of Ga(3+) is made possible by Pt-dissociated H species which spillover onto non-reducible Mg(Al)Ox or partially reducible Mg(Ga)(Al)Ox and undergo long-range transport over the support surface. Moderately mobile Ga(δ+)Ox migrates towards Pt clusters, where Ga(δ+) is only fully reduced to Ga(0) on condition of immediate stabilization inside Pt-Ga alloyed nanoparticles.

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Herein, we report the discovery of a toroidal inorganic cluster of zirconium(IV) oxysulfate of unprecedented size with the formula Zr 70 (SO 4) 58 (O/OH) 146 •x(H 2 O) (Zr 70), which displays different packing of ring units and thus several polymorphic crystal structures. The ring measures over 3 nm across, has an inner cavity of 1 nm and displays a pseudo-10-fold rotational symmetry of Zr 6 octahedra bridged by an additional Zr in the outer rim of the ring. Depending on the cocrystallizing species, the rings form various crystalline phases in which the torus units are connected in extended chain and network structures. One phase, in which the ring units are arranged in layers and form one-dimensional channels, displays high permanent porosity (BET surface area: 241 m 2 g À1), and thus demonstrates a functional property for potential use in, for example, adsorption or heterogeneous catalysis.

An optimal balance between a reasonable k-and R-space resolution should be obtained in order to adequately pinpoint the k-region of backscattering for each specific R-space peak.