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The dehydroaromatization of the naturally abundant methane is a promising process to produce aromatics and COx-free hydrogen. Low-temperature activity, regenerability and time-on-stream stability are fundamental challenges for the industrial use of the commonly studied benzenoid-selective Mo/HZSM-5 catalysts. We report a promotional effect of Nb doping on the activity and stability of Mo/HZSM-5 catalysts between 600 and 700 °C. Nb addition enhances benzene yields measurably at all investigated temperatures. An increased thermal stability of MoNb/HZSM-5 compared to Mo/HZSM-5 catalysts was found upon exposure to multiple consecutive reaction and oxidative treatment cycles, thus resulting in higher restorability of activity which extends the catalyst lifetime. While high-resolution electron microscopy showed homogeneous mixing of Mo and Nb on the catalyst, in situ time-resolved Mo K-edge X-ray absorption spectroscopy, supported by ex situ and time-resolved in situ near-ambient pressure X-ray photoelectron spectroscopy measurements, revealed a distinct interaction between the transition metals, involving a partial reduction of the otherwise stable Nb and concurrent oxidation of Mo which leads to increased stability of Mo5+/Mo4+ states. These effects were correlated to the enhanced activity and regenerability of the MoNb/HZSM-5 catalyst for methane dehydroaromatization. [ABSTRACT FROM AUTHOR]

Zr-based UiO-66 metal–organic frameworks are ideal platforms for the design and development of heterogeneous single-atom catalysts (SACs) because of their thermal and chemical stability with the presence of structural defects, enabling the introduction of isolated metal atoms. Elucidating the structure–reactivity relationships and understanding reaction mechanisms for these catalysts are crucial for their industrial applications. We focus here on these aspects for a technically important reaction, preferential CO oxidation (PROX) on a UiO-66-supported Cu SAC by following temperature perturbations in catalytic performance in correlation with changes in the electronic and adsorption properties, which are validated by comprehensive DFT computations. In situ DR-UV-VIS, XANES and NAP-XPS measurements indicated an increase of Cu1+-like states and partial reduction of ZrOx nodes with the increase in reaction temperature, which correlated with a decrease in PROX selectivity. Under similar conditions, DRIFTS measurements revealed a decay of COad adsorption on Cu (i.e., COad@Cu1+ species) and a corresponding red-shift under PROX conditions compared to CO oxidation, suggesting reduction-mediated charge transfer at the Cu–ZrOx interface. In contrast to the CO oxidation cycle which commences by CO adsorption on Cu1+-like sites, DFT computations revealed that the H2 oxidation cycle starts with the reaction of H2 with a pre-adsorbed O2 molecule on Cu1+-like sites, resulting in the generation of a H2O molecule and Cu2+-like sites, which are subsequently reduced to Cu1+-like sites through a successive reaction with a second H2 (or CO) molecule. Adsorption configurations and energies of CO and H2O co-adsorption indicated a competitive adsorption phenomenon on Cu species, which depends on the oxidation state of the Cu ion with a preference for CO adsorption on Cu1+-like sites, while H2O exhibits a stronger affinity for Cu2+-like sites. These results are discussed in terms of the reaction mechanism and PROX selectivity in Cu SAC catalysts and present a model for understanding the catalytic phenomena on MOF-supported SACs. [ABSTRACT FROM AUTHOR]

A protocol for efficient N-alkylation of benzamides with alcohols in the presence of cobalt-nanocatalysts is described. Key to the success of this general methodology is the use of highly dispersed cobalt nanoparticles supported on carbon, which are obtained from the pyrolysis of cobalt(II) acetate and o-phenylenediamine as a ligand at suitable temperatures. The catalytic material shows a broad substrate scope and good tolerance to functional groups. Apart from the synthesis of a variety of secondary amides (>45 products), the catalyst allows for the conversion of more challenging aliphatic alcohols and amides, including biobased and macromolecular amides. The practical applicability of the catalyst is underlined by the successful recycling and reusability. [ABSTRACT FROM AUTHOR]

A setup for dispersive X-ray absorption spectroscopy (XAS) with spatial, temporal and energy resolution is presented. Through investigation of a Mo/HZSM-5 catalyst during the dehydroaromatization of methane we observed a reduction gradient along the packed bed. Our new method represents an unprecedented addition to the analytical toolbox for in situ characterizations. [ABSTRACT FROM AUTHOR]

The pronounced effects of the composition of four-atom monometallic Cu and Pd and bimetallic CuPd clusters and the support on the catalytic activity and selectivity in the oxidative dehydrogenation of cyclohexene are reported. The ultra-nanocrystalline diamond supported clusters are highly active and dominantly produce benzene; some of the mixed clusters also produce cyclohexadiene, which are all clusters with a much suppressed combustion channel. The also highly active TiO2-supported tetramers solely produce benzene, without any combustion to CO2. The selectivity of the zirconia-supported mixed CuPd clusters and the monometallic Cu cluster is entirely different; though they are less active in comparison to clusters with other supports, these clusters produce significant fractions of cyclohexadiene, with their selectivity towards cyclohexadiene gradually increasing with the increasing number of copper atoms in the cluster, reaching about 50% for Cu3Pd1. The zirconia-supported copper tetramer stands out from among all the other tetramers in this reaction, with a selectivity towards cyclohexadiene of 70%, which far exceeds those of all the other cluster–support combinations. The findings from this study indicate a positive effect of copper on the stability of the mixed tetramers and potential new ways of fine-tuning catalyst performance by controlling the composition of the active site and via cluster–support interactions in complex oxidative reactions under the suppression of the undesired combustion of the feed. [ABSTRACT FROM AUTHOR]

Correction for 'Time-, space- and energy-resolved in situ characterization of catalysts by X-ray absorption spectroscopy' by Stefan Peters et al., Chem. Commun., 2023, 59, 12120–12123, https://doi.org/10.1039/D3CC03277A. [ABSTRACT FROM AUTHOR]

The synthesis of vitamin precursors via alkyne semi-hydrogenation has been achieved with a lead- and palladium-free catalyst. Cobalt nanoparticles modified by nitrogen doped carbon and supported on silica allow the production of a range of fine chemicals and vitamin precursors. The optimal catalyst could be conveniently recycled and used for at least five runs with consistent activity. Interestingly, this material selectively hydrogenates alkynes in the presence of easily reducible, cyano-, keto-, aldehyde-, and even nitro groups, which shows it to be a versatile catalyst for synthetic organic chemistry. [ABSTRACT FROM AUTHOR]

A convenient and practical diastereoselective cis-hydrogenation of multi-substituted pyridines and arenes is reported. Applying a novel heterogeneous ruthenium catalyst, the corresponding piperidines and cyclohexanes are obtained in high yields (typically >80%) with a good functional group tolerance under mild conditions. The robust ruthenium supported catalyst is smoothly prepared and can be reused multiple times without activity loss. [ABSTRACT FROM AUTHOR]

A general heterogeneous cobalt-catalysed CH-alkylation of indoles with alcohols is reported. Utilizing this straightforward borrowing hydrogen methodology, a series of substituted and functionalized indoles were easily coupled with benzylic, heterocyclic, and aliphatic alcohols including methanol to prepare >65 substituted indoles in good to excellent yields. The resulting products represent an interesting class of heterocyclic compounds widely used in organic synthesis and medicinal chemistry. Key for this synthesis is the use of specific cobalt-nanoparticles supported on N-doped carbon, which were conveniently prepared by the pyrolysis of a templated material generated in situ by mixing cobalt-nitrate, zinc-nitrate, 2,6-diaminopyridine, and colloidal silica, and subsequent removal of silica. [ABSTRACT FROM AUTHOR]

Catalytic hydrogenation of olefins using noble metal catalysts or pyrophoric RANEY® nickel is of high importance in the chemical industry. From the point of view of green and sustainable chemistry, design and development of Earth-abundant, less toxic, and more environmentally friendly catalysts are highly desirable. Herein, we report the convenient preparation of active cobalt catalysts and their application in hydrogenations of a wide range of terminal and internal carbon–carbon double bonds in water under mild conditions. Catalysts are prepared on multi-gram scale by pyrolysis of cobalt acetate and uracil, guanine, adenine or L -tryptophan. The most active material Co-Ura/C-600 showed good productivity in industrially relevant hydrogenation of diisobutene to isooctane and in natural oil hardening. [ABSTRACT FROM AUTHOR]

Catalytic CO oxidation is unveiled on size-selected Pt10 clusters deposited on two very different ultrathin (≈0.5–0.7 nm thick) alumina films: (i) a highly ordered alumina obtained under ultra-high vacuum (UHV) by oxidation of the NiAl(110) surface and (ii) amorphous alumina obtained by atomic layer deposition (ALD) on a silicon chip that is a close model of real-world supports. Notably, when exposed to realistic reaction conditions, the Pt10/UHV-alumina system undergoes a morphological transition in both the clusters and the substrate, and becomes closely akin to Pt10/ALD-alumina, thus reconciling UHV-type surface-science and real-world experiments. The Pt10 clusters, thoroughly characterized via combined experimental techniques and theoretical analysis, exhibit among the highest CO oxidation activity per Pt atom reported for CO oxidation catalysts, due to the interplay of ultra-small size and support effects. A coherent interdisciplinary picture then emerges for this catalytic system. [ABSTRACT FROM AUTHOR]

A protocol for efficient N -alkylation of benzamides with alcohols in the presence of cobalt-nanocatalysts is described. Key to the success of this general methodology is the use of highly dispersed cobalt nanoparticles supported on carbon, which are obtained from the pyrolysis of cobalt(ii) acetate and o -phenylenediamine as a ligand at suitable temperatures. The catalytic material shows a broad substrate scope and good tolerance to functional groups. Apart from the synthesis of a variety of secondary amides (>45 products), the catalyst allows for the conversion of more challenging aliphatic alcohols and amides, including biobased and macromolecular amides. The practical applicability of the catalyst is underlined by the successful recycling and reusability., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)