Tailored mesoporous silica supports for Ni catalysed hydrogen production from ethanol steam reforming

Mesoporous silica supported Ni nanoparticles have been investigated for hydrogen production from ethanol steam reforming. Ethanol reforming is structure-sensitive over Ni, and also dependent on support mesostructure; three-dimensional KIT-6 possessing interconnected mesopores offers superior metal dispersion, steam reforming activity, and on-stream stability against deactivation compared with a two-dimensional SBA-15 support

Diffusion NMR characterization of catalytic silica supports:a tortuous path

Mesoporous silicas have found widespread application within the field of heterogeneous catalysis. Acid functionalization of such materials, through one-pot or postsynthetic grafting of sulfonic acid groups, imparts activity for fatty acid esterification, with the studious choice of pore geometry facilitating significant rate enhancements. Diffusion NMR has been utilized for the first time to characterize the structure of mesoporous silicas through the transport behavior of systematically related carboxylic acids confined within their mesopore networks. A reduced diffusion coefficient is obtained for species constrained within the 3-dimensional interconnected pores of KIT-6 relative to the 2-dimensional noninterconnected pore channels of SBA-15. The effective tortuosity of both porous silicas increases with the acid chain length, with the diffusion behavior of long-chain acids dominated by the alkyl chain and silica architecture. Carboxylic acid diffusion within these two pore networks is unlikely to be rate-limiting in catalytic esterification over sulfonic acid silica analogues. Physicochemical insights from diffusion NMR will aid the future design of optimal silica architectures for catalytic applications

Tunable Silver-Functionalized Porous Frameworks for Antibacterial Applications

Healthcare-associated infections and the rise of drug-resistant bacteria pose significant challenges to existing antibiotic therapies. Silver nanocomposites are a promising solution to the current crisis, however their therapeutic application requires improved understanding of underpinning structure-function relationships. A family of chemically and structurally modified mesoporous SBA-15 silicas were synthesized as porous host matrices to tune the physicochemical properties of silver nanoparticles. Physicochemical characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES) and porosimetry demonstrate that functionalization by a titania monolayer and the incorporation of macroporosity both increase silver nanoparticle dispersion throughout the silica matrix, thereby promoting Ag₂CO₃ formation and the release of ionic silver in simulated tissue fluid. The Ag₂CO₃ concentration within functionalized porous architectures is a strong predictor for antibacterial efficacy against a broad spectrum of pathogens, including C. difficile and methicillin-resistant Staphylococcus aureus (MRSA)

Facile route to conformal hydrotalcite coatings over complex architectures:a hierarchically ordered nanoporous base catalyst for FAME production

An alkali- and nitrate-free hydrotalcite coating has been grafted onto the surface of a hierarchically ordered macroporous-mesoporous SBA-15 template via stepwise growth of conformal alumina adlayers and their subsequent reaction with magnesium methoxide. The resulting low dimensional hydrotalcite crystallites exhibit excellent per site activity for the base catalysed transesterification of glyceryl triolein with methanol for FAME production

Palladium-doped hierarchical ZSM-5 for catalytic selective oxidation of allylic and benzylic alcohols

From The Royal Society via Jisc Publications RouterHistory: received 2021-06-24, accepted 2021-08-17, collection 2021-10, pub-electronic 2021-10-20Article version: VoRPublication status: PublishedFunder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266; Grant(s): Nanoscience and Nanotechnology Facility, PR16195 - National Facility for XPS (“HarwellXPSFunder: Diamond Light Source; Id: http://dx.doi.org/10.13039/100011889; Grant(s): SP15151Hierarchical zeolites have the potential to provide a breakthrough in transport limitation, which hinders pristine microporous zeolites and thus may broaden their range of applications. We have explored the use of Pd-doped hierarchical ZSM-5 zeolites for aerobic selective oxidation (selox) of cinnamyl alcohol and benzyl alcohol to their corresponding aldehydes. Hierarchical ZSM-5 with differing acidity (H-form and Na-form) were employed and compared with two microporous ZSM-5 equivalents. Characterization of the four catalysts by X-ray diffraction, nitrogen porosimetry, NH3 temperature-programmed desorption, CO chemisorption, high-resolution scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy allowed investigation of their porosity, acidity, as well as Pd active sites. The incorporation of complementary mesoporosity, within the hierarchical zeolites, enhances both active site dispersion and PdO active site generation. Likewise, alcohol conversion was also improved with the presence of secondary mesoporosity, while strong Brønsted acidity, present solely within the H-form systems, negatively impacted overall selectivity through undesirable self-etherification. Therefore, tuning support porosity and acidity alongside active site dispersion is paramount for optimal aldehyde production

Impact of ceria support morphology on Au single-atom catalysts for benzyl alcohol selective oxidation

Alcohol oxidations are a key industrial chemical transformation, with aldehydes and ketones finding use in an array of applications. Nobel metals are known for their activity towards this chemoselective transformation, however, sustainable catalyst synthesis requires optimal utilisation of these scarce elements. Here, we report Au catalytic systems based on the deposition of isolated Au sites on different morphologies of ceria in which different surface facets of the support are exposed. Through tailoring the support morphology and from extensive catalyst characterisation, it is shown that the exposed facet is critical for controlling the formation (or not) of isolated Au sites. Both the 110 and 111 facets are capable of this feat, yielding single-atom sites for rod, octahedron, and polyhedron morphologies. In contrast, the 100 facet is not, resulting in Au nanoparticles on cubic ceria. This dictation over Au species is critical to benzyl alcohol oxidation capacity at mild conditions and in the absence of a soluble base, with only single-atom catalyst (SAC) systems demonstrating activity. Furthermore, the exposed surface facet also governs the degree of surface oxygen vacancies, which is critical to catalyst activity and arises from its control over substrate adsorption strength, as revealed through T1/T2 NMR relaxation measurements

Shining light on the solid–liquid interface: in situ/operando monitoring of surface catalysis

Many industrially important chemical transformations occur at the interface between a solid catalyst and liquid reactants, despite which relatively little attention has been paid to spectroscopic methods for interrogating the working solid–liquid interface. This partly reflects a limited number of analytical techniques that give access to interface-specific information. Direct observation of surface species at catalytic solid–liquid interfaces is a daunting challenge for many in situ techniques due to the low concentration and/or short lifetime of chemical species in dynamic reactions. This review discusses the application of in situ and operando spectroscopies to probe solid–liquid interfaces, with a focus on the resulting mechanistic insight in the context of catalysis for sustainable chemistry

In-situ X-ray studies of clean catalytic technologies

The rational design of new heterogeneous catalysts for clean chemical technologies can be accelerated by molecular level insight into surface chemical processes. In-situ methodologies, able to provide time-resolved and/or pressure dependent information on the evolution of reacting adsorbed layers over catalytically relevant surfaces, are therefore of especial interest. Here we discuss the application of in-situ XPS and in-situ, synchronous DRIFTS/MS/XAS methodologies to elucidate the active site in Pd-catalyzed, selective aerobic oxidation of allylic alcohols