High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone.

The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method.

CaO as drop-in colloidal catalysts for the synthesis of higher polyglycerols.

Glycerol is an attractive renewable building block for the synthesis of polyglycerols, which find application in the cosmetic and pharmaceutical industries. The selective etherification of glycerol to higher oligomers was studied in the presence of CaO colloids and the data are compared with those obtained from NaOH and CaO. The materials were prepared by dispersing CaO, CaCO3 , or Ca(OH)2 onto a carbon nanofiber (CNF) support.

Differences in the location of guest molecules within zeolite pores as revealed by multilaser excitation confocal fluorescence microscopy: which molecule is where?

A detailed and systematic polarized confocal fluorescence microscopy investigation is presented on three batches of large coffin-shaped ZSM-5 crystals (i.e., parent, steamed at 500 °C, and steamed at 700 °C).

Mapping metals incorporation of a whole single catalyst particle using element specific X-ray nanotomography.

Full-field transmission X-ray microscopy has been used to determine the 3D structure of a whole individual fluid catalytic cracking (FCC) particle at high spatial resolution and in a fast, noninvasive manner, maintaining the full integrity of the particle. Using X-ray absorption mosaic imaging to combine multiple fields of view, computed tomography was performed to visualize the macropore structure of the catalyst and its availability for mass transport. We mapped the relative spatial distributions of Ni and Fe using multiple-energy tomography at the respective X-ray absorption K-edges and correlated these distributions with porosity and permeability of an equilibrated catalyst (E-cat) particle.

Differences in single and aggregated nanoparticle plasmon spectroscopy.

Vibrational spectroscopy usually provides structural information averaged over many molecules. We report a larger peak position variation and reproducibly smaller FWHM of TERS spectra compared to SERS spectra indicating that the number of molecules excited in a TERS experiment is extremely low. Thus, orientational averaging effects are suppressed and micro ensembles are investigated.

High-resolution single-molecule fluorescence imaging of zeolite aggregates within real-life fluid catalytic cracking particles.

Fluid catalytic cracking (FCC) is a major process in oil refineries to produce gasoline and base chemicals from crude oil fractions. The spatial distribution and acidity of zeolite aggregates embedded within the 50-150 μm-sized FCC spheres heavily influence their catalytic performance. Single-molecule fluorescence-based imaging methods, namely nanometer accuracy by stochastic chemical reactions (NASCA) and super-resolution optical fluctuation imaging (SOFI) were used to study the catalytic activity of sub-micrometer zeolite ZSM-5 domains within real-life FCC catalyst particles.

Aluminum-phosphate binder formation in zeolites as probed with X-ray absorption microscopy.

In this work, three industrially relevant zeolites with framework topologies of MOR, FAU and FER have been explored on their ability to form an AlPO4 phase by reaction of a phosphate precursor with expelled framework aluminum. A detailed study was performed on zeolite H-mordenite, using in situ STXM and soft X-ray absorption tomography, complemented with (27)Al and (31)P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, XRD, FT-IR spectroscopy, and N2 physisorption. Extraframework aluminum was extracted from steam-dealuminated H-mordenite and shown to dominantly consist of amorphous AlO(OH).

Hexane cracking over steamed phosphated zeolite H-ZSM-5: promotional effect on catalyst performance and stability.

The nature behind the promotional effect of phosphorus on the catalytic performance and hydrothermal stability of zeolite H-ZSM-5 has been studied using a combination of (27) Al and (31) P MAS NMR spectroscopy, soft X-ray absorption tomography and n-hexane catalytic cracking, complemented with NH3 temperature-programmed desorption and N2 physisorption. Phosphated H-ZSM-5 retains more acid sites and catalytic cracking activity after steam treatment than its non-phosphated counterpart, while the selectivity towards propylene is improved. It was established that the stabilization effect is twofold.

Experimental and computational evidence for the mechanism of intradiol catechol dioxygenation by non-heme iron(III) complexes.

Catechol intradiol dioxygenation is a unique reaction catalyzed by iron-dependent enzymes and non-heme iron(III) complexes. The mechanism by which these systems activate dioxygen in this important metabolic process remains controversial. Using a combination of kinetic measurements and computational modelling of multiple iron(III) catecholato complexes, we have elucidated the catechol cleavage mechanism and show that oxygen binds the iron center by partial dissociation of the substrate from the iron complex.

Selective staining of Brønsted acidity in zeolite ZSM-5-based catalyst extrudates using thiophene as a probe.

Optical absorption and confocal fluorescence micro-spectroscopy were applied to investigate Brønsted acidity in millimetre-sized extrudates of Na(H)-ZSM-5 and SiO2 with varying ZSM-5 content. Partially (residual Na present) and fully proton-exchanged extrudates were employed, using thiophene oligomerization as a probe reaction. Time-resolved in situ optical absorption spectra and time dependent DFT calculations revealed several initial reaction pathways during the oligomerization reaction.

Effect of preparation method and CuO promotion in the conversion of ethanol into 1,3-butadiene over SiO₂-MgO catalysts.

Silica-magnesia (Si/Mg=1:1) catalysts were studied in the one-pot conversion of ethanol to butadiene. The catalyst synthesis method was found to greatly influence morphology and performance, with materials prepared through wet-kneading performing best both in terms of ethanol conversion and butadiene yield. Detailed characterization of the catalysts synthesized through co-precipitation or wet-kneading allowed correlation of activity and selectivity with morphology, textural properties, crystallinity, and acidity/basicity.

Breakthroughs in hard X-ray diffraction: towards a multiscale science approach in heterogeneous catalysis.

: Modern heterogeneous catalysis would benefit from a multiscale science approach bridging the molecular world with the macroscopic world. Because of recent breakthroughs in X‐ray diffraction methods, including the surface X‐ray diffraction of atomically flat model catalysts, X‐ray diffraction tomography of catalyst bodies, and X‐ray profiling of an active catalyst in a chemical reactor, such an approach is now within reach.[Image: see text]

Platinum-promoted Ga/Al₂O₃ as highly active, selective, and stable catalyst for the dehydrogenation of propane.

A novel catalyst material for the selective dehydrogenation of propane is presented. The catalyst consists of 1000 ppm Pt, 3 wt% Ga, and 0.25 wt% K supported on alumina.

Reactivity Descriptor in Solid Acid Catalysis: Predicting Turnover Frequencies for Propene Methylation in Zeotypes.

Recent work has reported the discovery of metal surface catalysts by employing a descriptor-based approach, establishing a correlation between a few well-defined properties of a material and its catalytic activity. This theoretical work aims for a similar approach in solid acid catalysis, focusing on the reaction between propene and methanol catalyzed by Brønsted acidic zeotype catalysts. Experimentally, the ammonia heat of adsorption is often used as a measure of the strength of acid sites.

Dispersion and orientation of zeolite ZSM-5 crystallites within a fluid catalytic cracking catalyst particle.

Confocal fluorescence microscopy was employed to selectively visualize the dispersion and orientation of zeolite ZSM-5 domains inside a single industrially applied fluid catalytic cracking (FCC) catalyst particle. Large ZSM-5 crystals served as a model system together with the acid-catalyzed fluorostyrene oligomerization reaction to study the interaction of plane-polarized light with these anisotropic zeolite crystals. The distinction between zeolite and binder material, such as alumina, silica, and clay, within an individual FCC particle was achieved by utilizing the anisotropic nature of emitted fluorescence light arising from the entrapped fluorostyrene-derived carbocations inside the zeolite channels.

Recent advances in secondary ion mass spectrometry of solid acid catalysts: large zeolite crystals under bombardment.

This Perspective aims to inform the heterogeneous catalysis and materials science community about the recent advances in Time-of-Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) to characterize catalytic solids by taking large model H-ZSM-5 zeolite crystals as a showcase system. SIMS-based techniques have been explored in the 1980-1990's to study porous catalyst materials but, due to their limited spectral and spatiotemporal resolution, there was no real major breakthrough at that time. The technical advancements in SIMS instruments, namely improved ion gun design and new mass analyser concepts, nowadays allow for a much more detailed analysis of surface species relevant to catalytic action.

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites.

In order to elucidate phosphorus-zeolite H-ZSM-5 interactions, a variety of phosphorus-modified zeolite H-ZSM-5 materials were studied in a multi-spectroscopic manner. By deploying single pulse (27)Al, (31)P MAS NMR, 2D heteronuclear (27)Al-(31)P correlation (HETCOR), (27)Al MQ MAS NMR spectroscopy, TPD of pyridine monitored by FT-IR spectroscopy, and Scanning Transmission X-ray Microscopy (STXM) the interplay and influence of acidity, thermal treatment and phosphorus on the structure and acidity of H-ZSM-5 were established. It was found that while acid treatment did not affect the zeolite structure, thermal treatment leads to the breaking of Si-OH-Al bonds, a decrease in the strong acid site number and the formation of terminal Al-OH groups.

Phosphatation of zeolite H-ZSM-5: a combined microscopy and spectroscopy study.

A variety of phosphated zeolite H-ZSM-5 samples are investigated by using a combination of Fourier transfer infrared (FTIR) spectroscopy, single pulse (27)Al, (29)Si, (31)P, (1)H-(31)P cross polarization (CP), (27)Al-(31)P CP, and (27)Al 3Q magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, scanning transmission X-ray microscopy (STXM) and N2 physisorption. This approach leads to insights into the physicochemical processes that take place during phosphatation. Direct phosphatation of H-ZSM-5 promotes zeolite aggregation, as phosphorus does not penetrate deep into the zeolite material and is mostly found on and close to the outer surface of the zeolite, acting as a glue.

Identification of intermediates in zeolite-catalyzed reactions by in situ UV/Vis microspectroscopy and a complementary set of molecular simulations.

The optical absorption properties of (poly)aromatic hydrocarbons occluded in a nanoporous environment were investigated by theoretical and experimental methods. The carbonaceous species are an essential part of a working catalyst for the methanol-to-olefins (MTO) process. In situ UV/Vis microscopy measurements on methanol conversion over the acidic solid catalysts H-SAPO-34 and H-SSZ-13 revealed the growth of various broad absorption bands around 400, 480, and 580 nm.