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Rigorous comparisons between single site-and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed CuS/ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The CuS/ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed CuN/ZSM-5) in the oxidation of NH3 to N2, with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the CuS/ZSM-5 catalyst. [ABSTRACT FROM AUTHOR]

We demonstrate a modified sol‐immobilization procedure using (MeOH)x/(H2O)1‐x solvent mixtures to prepare Pd/TiO2 catalysts that are able to reduce the formation of acid catalyzed products, e. g. ethers, for the hydrogenation of furfural. Transmission electron microscopy found a significant increase in polyvinyl alcohol (PVA) deposition at the metal‐support interface and temperature programmed reduction found a reduced uptake of hydrogen, compared to an established Pd/TiO2 preparation. We propose that the additional PVA hinders hydrogen spillover onto the TiO2 support and limits the formation of Brønsted acid sites, required to produce ethers. Elsewhere, the new preparation route was able to successfully anchor colloidal Pd to the TiO2 surface, without the need for acidification. This work demonstrates the potential for minimizing process steps as well as optimizing catalyst selectivity – both important objectives for sustainable chemistry. [ABSTRACT FROM AUTHOR]

The aqueous phase reforming of glycerol, to hydrogen, alkanes and liquid phase dehydration/dehydrogenation products, was studied over a series of 1 wt% Pt/LaMO3 (where M = Al, Cr, Mn, Fe, Co, Ni) catalysts and compared to a standard 1 wt% Pt/γ-Al2O3 catalyst. The sol–gel combustion synthesis of lanthanum-based perovskites LaMO3 produced pure phase perovskites with surface areas of 8–18 m2g−1. Glycerol conversions were higher than the Pt/γ-Al2O3 (10%) for several perovskite supported catalysts, with the highest being for Pt/LaNiO3 (19%). Perovskite-based catalysts showed reduced alkane formation and significantly increased lactic acid formation compared to the standard catalyst. However, most of the perovskite materials undergo phase separation to LaCO3OH and respective M site oxides with Pt particle migration. The exception being the LaCrO3 support which was found to remain structurally stable. Catalytic performance remained stable over several cycles, for catalysts M = Al, Cr and Ni, despite phase separation of some of these materials. Materials where M site leaching into solution was observed (M = Mn and Co), were found to be catalytically unstable, which was hypothesised to be due to significant loss in support surface area and uncontrolled migration of Pt to the remaining support surface. In the case of Pt/LaNiO3 alloying between the exsoluted Ni and Pt was observed post reaction. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is a sustainable method for producing hydrogen―the ultimate clean energy carrier. However, high cost and poor stability of the Pt catalyst for hydrogen evolution reaction (HER) hinder its wide applications. Here, we report a facile approach to synthesize an ultra-low PtCo bimetallic catalyst embedded in porous carbon via direct annealing of Pt-doped ZIF-67. The resulting catalyst (CPt@ZIF-67) with only 5 wt% Pt loading exhibits better performance than commercial 20 wt% Pt/C, achieving a Tafel slope of 27.1 mV dec−1 with an overpotential of only 50 mV at current density of 10 mA cm−2. Theoretical simulations show that carbon cages generated over the bimetal clusters during annealing dramatically reduce the free energy for HER. The free energy does not reduce proportionally with increasing Pt loading, implying the need to ensure appropriate Pt placement on surfaces, rather than simply raising Pt level, in order to enhance effectiveness of a Pt-based catalyst. The study provides a viable approach for developing cost-effective Pt-related catalysts for HER. [ABSTRACT FROM AUTHOR]

Monometallic and bimetallic tin-containing framework architectures have been prepared by hydrothermal methods. Structural and spectroscopic techniques were used to probe the nature of the solid-acid sites, at the molecular level, using a combination of XRD, DR UV-Vis, solid state MAS NMR (119Sn, 27Al and 31P) and XAFS. The nature and strength of the solid-acid sites were experimentally probed by FT-IR spectroscopy using CD3CN as a probe molecule. To elucidate further the local-structure, the structural characteristics of the Sn sites were probed using DFT calculations, with a view to rationalising the experimental findings. These detailed structural and spectroscopic studies revealed the presence of multiple Sn environments, with the monometallic SnAlPO-5 catalyst displaying a greater number of tetrahedral Sn(iv) active centres. These framework Sn(iv) centres generated strong Lewis acid sites, when compared with their bimetallic Co–Sn analogue, thereby affording attractive possibilities for modulating catalytic reactivity. [ABSTRACT FROM AUTHOR]

The quality of methylene diphenyl diisocyanate (MDI)products,which are valuable feedstocks in the industrial manufacture of polyurethanes,can be compromised by the presence of color, presumed to arise fromtrace impurities. One undesired branch in the synthesis chain originateswith phosgenation of diaryl ureas, formed from reactions between arylisocyanates and polyamine precursors. Subsequent key steps include,(i) breakdown of the primary compounds, substituted chloroformamidine-N-carbonyl chlorides (CCC), to give aryl isocyanide dichlorides,ArNCCl2, (ii) an apparent equilibrium connecting CCC witharyl carbodiimides, and (iii) the thermolysis of ArNCCl2in the presence of MDI. Color formation is associated directly withthe last process; it involves several events, including HCl eliminationfrom reaction of ArNCCl2and MDI, formation of carbon-centeredradicals, and a contribution from oxidation at the methylene bridge. [ABSTRACT FROM AUTHOR]

Phenyl and 4-methylphenyl isocyanide dichlorides aremodels forbyproduct that may be formed in the later stages of certain polyurethaneproduction chains. Photochemical electron paramagnetic resonance (EPR)studies (λ > 310 nm), using the spin trap, N-tert-butyl-α-phenylnitrone, confirm a previouslymade suggestion that ArNCCl2can behave as a chlorineradical source. EPR spectra recorded during and after irradiationand supported by simulations evolve over time and indicate formationof the short-lived spin trap–Cl•adduct anda longer lived benzoyl-N-tert-butylnitroxideradical. Photolysis of C6H5NCCl2, either alone or mixed with methylene diaryl isocyanate species,in o-C6H4Cl2, apolyurethane process solvent, led to the formation of mixtures containingdichloro- and trichlorobiphenyl isomers. [ABSTRACT FROM AUTHOR]

Rigorous comparisons between single site-and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed CuS/ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The CuS/ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed CuN/ZSM-5) in the oxidation of NH3 to N2, with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the CuS/ZSM-5 catalyst. [ABSTRACT FROM AUTHOR]

We demonstrate a modified sol‐immobilization procedure using (MeOH)x/(H2O)1‐x solvent mixtures to prepare Pd/TiO2 catalysts that are able to reduce the formation of acid catalyzed products, e. g. ethers, for the hydrogenation of furfural. Transmission electron microscopy found a significant increase in polyvinyl alcohol (PVA) deposition at the metal‐support interface and temperature programmed reduction found a reduced uptake of hydrogen, compared to an established Pd/TiO2 preparation. We propose that the additional PVA hinders hydrogen spillover onto the TiO2 support and limits the formation of Brønsted acid sites, required to produce ethers. Elsewhere, the new preparation route was able to successfully anchor colloidal Pd to the TiO2 surface, without the need for acidification. This work demonstrates the potential for minimizing process steps as well as optimizing catalyst selectivity – both important objectives for sustainable chemistry. [ABSTRACT FROM AUTHOR]

Rigorous comparisons between single site- and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed Cu S /ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The Cu S /ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed Cu N /ZSM-5) in the oxidation of NH 3 to N 2 , with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the Cu S /ZSM-5 catalyst., Competing Interests: Competing interests statement:The authors declare no competing interest.