Copper nanoparticles supported on zirconia (Cu/ZrO) or related supported oxides (Cu/ZrO/SiO) show promising activity and selectivity for the hydrogenation of CO to CHOH. However, the role of the support remains controversial because most spectroscopic techniques provide information dominated by the bulk, making interpretation and formulation of structure-activity relationships challenging. In order to understand the role of the support and in particular of the Zr surface species at a molecular level, a surface organometallic chemistry approach has been used to tailor a silica support containing isolated Zr(IV) surface sites, on which copper nanoparticles (∼3 nm) are generated. These supported Cu nanoparticles exhibit increased CHOH activity and selectivity compared to those supported on SiO, reaching catalytic performances comparable to those of the corresponding Cu/ZrO. Ex situ and in situ X-ray absorption spectroscopy reveals that the Zr sites on silica remain isolated and in their +4 oxidation state, while ex situ solid-state nuclear magnetic resonance spectroscopy and catalytic performances show that similar mechanisms are involved with the single-site support and ZrO. These observations imply that Zr(IV) surface sites at the periphery of Cu particles are responsible for promoting CHOH formation on Cu-Zr-based catalysts and provide a guideline to develop selective CHOH synthesis catalysts.

Sn-β zeolites prepared using different recipes feature very different catalytic activity for aqueous phase glucose isomerization, suggesting the presence of different active sites. A systematic study of the morphology and atomic-level structure of the materials using DNP NMR spectroscopy in combination with first principles calculations allows for the discrimination between potential sites and 2 leads to a proposal of specific structural features that are important for high activity. The results indicate that the materials showing highest activity posses a highly hydrophobic, defect-free zeolite framework. Those materials show so-called closed and associated partially hydrolyzed Sn(IV)-sites in the T6 and T5/T7 lattice position. On the other hand post-synthetically synthesized Sn-b samples prepared in two steps via dealumination and subsequent solid-state ion-exchange from Al-b show significant lower activity which is associated with a hydrophilic framework and/or a lower accessibility and lattice position of the Sn sites in the zeolite crystal. Further we provide a method to distinguish between different Sn sites based on NMR cartography using chemical shift and chemical shift anisotropy as readily measurable parameters. This cartography not only allows identifying the nature of the active sites (closed, defect-open and hydrolyzed-open), but also their position within the BEA framework.

Dynamic nuclear polarization surface enhanced NMR (DNP-SENS), Mössbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active-site speciation in Sn-β zeolite. This approach unambiguously shows the presence of framework Sn(IV)-active sites in an octahedral environment, which probably correspond to so-called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework).

A two-step procedure for the post-synthetic preparation of Lewis acidic Sn-, Zr- and Ti-zeolite β is reported. Dealumination of a commercially available Al-β zeolite leads to the formation of highly siliceous material containing silanol nests, which can be filled in a second step via the solid-state ion-exchange or impregnation of an appropriate metal precursor. Spectroscopic studies indicate that each metal is subsequently coordinated within the zeolite framework, and that little or no bulk oxides are formed--despite the high metal loadings. The synthesised catalysts demonstrate excellent activity for the isomerisation of glyceraldehyde to dihydroxyacetone, a key model reaction for the upgrading of bio-renewable feedstocks, and the epoxidation of bulky olefins.

Selective hydrogenation of CO2 into methanol is a key sustainable technology, where Cu/Al2O3 prepared by surface organometallic chemistry displays high activity towards CO2 hydrogenation compared to Cu/SiO2, yielding CH3OH, dimethyl ether (DME), and CO. CH3OH formation rate increases due to the metal–oxide interface and involves formate intermediates according to advanced spectroscopy and DFT calculations. Al2O3 promotes the subsequent conversion of CH3OH to DME, showing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place 1) directly by activation of CO2 at the metal–oxide interface, and 2) indirectly by the conversion of formate surface species and CH3OH to methyl formate, which is further decomposed into CH3OH and CO. This study shows how Al2O3, a Lewis acidic and non‐reducible support, can promote CO2 hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal–oxide interface.

In recent years, the on-purpose production of 1,3-butadiene (BD) from renewable resources such as ethanol has received increased attention. In that context, Lewis acid catalysts play an important role, especially in the two-step process, i.e. when a mixture of acetaldehyde and ethanol is used as substrate. As the reaction mechanism consists of many intermediates and occurs over different catalytic functionalities, it is notoriously difficult to gain molecular-level insights into the mechanism. Here, we present a study on Lewis acidic Ta-BEA and propose a plausible reaction mechanism. We developed an operando DRIFTS-MS setup that allows for precise control and analysis of changes in the gas-phase composition as well as surface species. Using this tool, we found a surface intermediate with a vibrational frequency at 1690 cm–1 that is only formed in the presence of both ethanol and crotonaldehyde and that is likely involved in the production of BD. Our data further suggests that a subtle control of the ratio of ethanol to acetaldehyde is crucial to keep a high ethoxy coverage and to desorb the intermediate crotyl alcohol in order to achieve high BD productivity. To the best of our knowledge, this is the first dynamic operando spectroscopic study on this re-emerging reaction.

CuGax alloy nanoparticles supported on SiO2 can be obtained by surface organometallic chemistry. This catalyst is active and selective for the hydrogenation of CO2 to CH3OH, related to the formation of an optimal interface between Cu and GaIIIOx.

Dynamic nuclear polarization surface enhanced NMR (DNP-SENS), Mçssbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active-site speciation in Sn-b zeolite. This approach unambiguously shows the presence of framework Sn IV -active sites in an octahedral environment, which probably correspond to so-called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework).Heterogeneous catalysts with well-defined isolated active sites do not only facilitate mechanistic investigations, but can also show unparalleled activity in a variety of important reactions. One example is TS-1 for the epoxidation of propene with H 2 O 2 .[1] A more recent example is Sn-b, which consists of Sn IV -sites embedded in the zeolite-b framework. [2] The uniform distribution of isolated Lewis acid sites, in combination with the unique hydrophobic pore architecture of the material, results in an unrivalled catalytic performance. Of particular interest is the Lewis acid-catalyzed isomerization and epimerization of sugars, key transformations in the upgrading of cellulose-based renewable feedstocks. [3] Sn-b is also active for other reactions, including the Baeyer-Villiger oxidation of ketones and aldehydes, [4] the carbonylene cyclization of citronellal, [5] and the Meerwein-Ponndorf-Verley-Oppenauer reaction. [6] Today, Sn-b can be conveniently synthesized with Sn-loadings varying between 0 and 10 wt %. [7] [*] P. Wolf, [+] M. Valla, [+] Dr. A. Comas-Vives, [+] Dr.