Zeolite Structural Confinement Effects Enhance One-Pot Catalytic Conversion of Ethanol to Butadiene

Confining Bismuth-Halide Perovskite in Mesochannels of Silica Nanomembranes for Exceptional Photocatalytic Abatement of Air Pollutants

Spatially confined photocatalysis has emerged as a viable strategy for the intensification of various redox reactions, but the influence of confined structure on reaction behavior is always overlooked in gas-solid reactions. Herein, we report a nanomembrane with confining Cs3 Bi2 Br9 nanocrystals inside vertical channels of porous insulated silica thin sheets (CBB@SBA(⊥)) for photocatalytic nitric oxide (NO) abatement. The ordered one-dimensional (1D) pore channels with mere 70 nm channel length provide a highly accessible confined space for catalytic reactions. A record-breaking NO conversion efficiency of 98.2 % under a weight hourly space velocity (WHSV) of 3.0×106  mL g-1  h-1 , as well as exceptionally high stability over 14 h and durability over a wide humidity range (RH=15-90 %) was realized over SBA(⊥) confined Cs3 Bi2 Br9 , well beyond its nonconfined analogue and the Cs3 Bi2 Br9 confine in Santa Barbara Amorphous (SBA-15). Mechanism studies suggested that the insulated pore channels of SBA(⊥) in CBB@SBA(⊥) endow concentrated electron field and enhanced mass transfer that render high exposure of reactive species and lower reaction barrier needs for ⋅O2 - formation and NO oxidation, as well as prevents structural degradation of Cs3 Bi2 Br9 . This work expands an innovative strategy for designing efficient photocatalysts for air pollution remediation.

Self-Organization of 1-Propanol at H-ZSM-5 Brønsted Acid Sites

In situ Al K-edge X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) spectroscopy in conjunction with ab initio molecular dynamics (AIMD) simulations show that adsorption of 1-propanol alters the structure of the Brønsted acid site through changes in the associated aluminum-oxygen tetrahedron in zeolite H-MFI. The decreasing intensity of the pre-edge signal of the in situ Al K-edge XANES spectra with increasing 1-propanol coverage shows that Al T-sites become more symmetric as the sorbed alcohol molecules form monomers, dimers, and trimers. The adsorption of monomeric 1-propanol on Brønsted acid sites reduces the distortion of the associated Al T-site, shortens the Al-O distance, and causes the formation of a Zundel-like structure. With dimeric and trimeric alcohol clusters, the zeolite proton is fully transferred to the alcohols and the aluminum-oxygen tetrahedron becomes fully symmetric. The subtle changes in Al-K-edge XANES in the presence of sorbate structures, with the use of theory, are used to probe the local zeolite structures and provide a basis to predict the population and chemical state of the sorbed species.

Room temperature removal of high-space-velocity formaldehyde boosted by fixing Pt nanoparticles into Beta zeolite framework

Catalytic oxidation of volatile organic compounds like formaldehyde (HCHO) over the noble metals catalysts at room temperature is among the most promising strategies to control indoor pollution but remains one challenge to maximize the efficiency of noble metal species. Herein, we demonstrated the straightforward encapsulation of highly dispersive Pt nanoparticles (NPs) within BEA zeolite and adjacent with the surface hydroxyl groups to reach the synergistic HCHO oxidation at 25 °C. High efficiency and long-term stability was reached under large space velocity (∼100% conversion at 180,000 mL (g_cat × h)^-1 and >95% at 360,000 mL (g_cat × h)^-1), affording rapid elimination rate of 129.4 μmol (g_Pt × s)^-1 and large turnover frequency of 2.5 × 10^-2 s^-1. This is the first synergy example derived from the hydroxyl groups and confined noble metals within zeolites that accelerated the rate-determining step, the formate transformation, in the HCHO elimination.

Research progress of catalysts for aldol condensation of biomass based compounds

Research progress of catalysts of the aldol condensation reaction of biomass based compounds is summarized for the synthesis of liquid fuel precursors and chemicals. In summary, an acidic catalyst, alkaline catalyst, acid–base amphoteric catalyst, ionic liquid and other catalysts can catalyze the aldol condensation reaction. The aldol condensation reaction catalyzed by an acid catalyst has the problems of low conversion and low yield. The basic catalyst catalyzes the aldol condensation reaction with high conversion and yield, but the existence of liquid alkali is difficult to separate from the product. The reaction temperature needed for oxide and hydrotalcite alkali is relatively high. The basic resin has good catalytic activity and at a low reaction temperature, and is easy to separate from the target product. Acid–base amphoteric catalysts have received extensive attention from researchers for their excellent activity and selectivity. Ionic liquid is a new type of material, which can also be used for the aldol condensation reaction. In the future application of aldol condensation, the development of strong alkaline resin is a good research direction.

Research progress of catalysts of the aldol condensation reaction of biomass based compounds is summarized for the synthesis of liquid fuel precursors and chemicals.

Enhanced Performance and Stability of a Trimetallic CuZnY/SiBEA Catalyst in Ethanol to Butadiene Reaction by Introducing Copper to Optimize Acid/Base Ratio

Bioethanol to butadiene is currently the most promising non-oil-based butadiene production route. Here, copper is introduced into the conventional bimetallic zeolite catalyst to partially substitute for zinc; the isolated tetracoordinated Cu(II) species are formed, with weak and strong basic sites transformed into medium acid sites in trimetallic CuZnY/SiBEA catalyst. A partial substitution of zinc by copper increases the dispersion of metal, reduces the formation of ZnO clusters, decreases the pore blockage, and enhances the total pore volume of catalyst. The Cu1Zn2Y5/SiBEA catalyst with an appropriate 0.33 Cu/(Cu + Zn) mass ratio, a highest medium acid sites/(weak + strong) basic sites value of 6.17, and largest total pore volume of 0.251 cm3/g in all samples presents excellent catalytic performance in the ethanol to butadiene reaction: 99.01% ethanol conversion and 73.36% butadiene selectivity, higher than most reported ethanol to butadiene catalysts. The isolated tetracoordinated Cu(II) structure is stable, which is beneficial to the stability of trimetallic catalyst; when the reaction time is 60 h, the butadiene selectivity is 45.95%, 14% higher than corresponding bimetallic catalyst. The butadiene productivity of Cu1Zn2Y5/SiBEA catalyst reaches up to 1.68 gBD·gcat−1·h−1 at WHSV = 6 h−1 and time-on-stream = 8 h. Increasing reaction temperature could linearly increase the ethanol conversion, while the butadiene selectivity increases first and then decreases, the suitable temperature is 375 ℃ for the highest butadiene yield.

Confinement in a Zeolite and Zeolite Catalysis

ConspectusZeolites, accompanied by their initial discovery as natural mines and the subsequent large-scale commercial production, have played indispensable roles in various fields such as petroleum refining and the chemical industry. Understanding the characteristics of zeolites, in contrast to their counterparts with similar chemical compositions and the origin thereof, is always a hot and challenging topic. Zeolites are known as intrinsic confined systems with ordered channels on the molecular scale, and structural confinement has been proposed to explain the unique chemical behaviors of zeolites. Generally, the channels of zeolites can regulate the diffusion of molecules, leading to a visible difference in molecular transportation and the ultimate shape-selective catalysis. On the other hand, the local electric field within the zeolite channels or cages can act on the guest molecules and change their energy levels. Confinement can be simply interpreted from both spatial and electronic issues; however, the nature of zeolite confinement is ambiguous and needs to be clarified.In this Account, we make a concise summary and analysis of the topics of confinement in a zeolite and zeolite catalysis from two specific views of spatial constraint and a local electric field to answer two basic questions of why zeolites and what else can we do with zeolites. First, it is shown how to construct functional sites including Brønsted acid sites, Lewis acid sites, extraframework cation sites, and entrapped metal or oxide aggregates in zeolites via confinement and how to understand the specific role of confinement in their reactivity. Second, the multiple impacts of confinement in zeolite-catalyzed reactions are discussed, which rationally lead to several unique processes, namely, Brønsted acid catalysis confined in zeolites, Lewis acid catalysis confined in zeolites, catalysis by zeolite-confined coordinatively unsaturated cation sites, and a cascade reaction within the confined space of zeolites. Overall, confinement effects do exist in zeolite systems and have already played extremely important roles in adsorption and catalysis. Although confinement might exist in many systems, the confinement by zeolites is more straightforward thanks to their well-ordered and rigid structure, deriving unique chemical behaviors within the confined space of zeolites. A zeolite is a fantastic scaffold for constructing isolated sites spatially and electrostatically confined in its matrix. Furthermore, zeolites containing well-defined transition-metal sites can be treated as inorganometallic complexes (i.e., a zeolite framework as the ligand of transition-metal ions) and can catalyze reactions resembling organometallic complexes or even metalloenzymes. The local electric field within the confined space of zeolites is strong enough to induce or assist the activation of small molecules, following the working fashion of frustrated Lewis pairs. The tactful utilization of structural confinement, both spatially and electronically, becomes the key to robust zeolites for adsorption and catalysis.

Insights into the synergistic effect of active centers over ZnMg/SBA-15 catalysts in direct synthesis of butadiene from ethanol

Functionalized catalysts with multiple active centers have been studied for direct conversion of ethanol to butadiene (ETB).

Recent Advances in Catalysts for the Conversion of Ethanol to Butadiene

Butadiene is an important monomer for synthetic rubbers. Currently, the annual demand of ∼16 million tonnes is satisfied by butadiene produced as a byproduct of steam naphtha cracking where ethylene and propylene are the main products. The availability of large amounts of shale gas and condensates in the USA since about 2008 has led to a change in the cracker feed from naphtha to ethane and propane, affecting the amount of butadiene obtained. This has provided the impetus to look into direct processes for butadiene production. One option is the eco-friendly conversion of (bio) ethanol to butadiene (ETB). This process had been developed in the 1930s in the then Soviet Union. It was operated on a large scale in USA during World War II but has since been abandoned in favour of petroleum-based processes. The current trend, driven both by the availability of the raw material and ecological considerations, may make this process feasible again, particularly if the catalytic systems can be improved. This critical review discusses recent catalysts for the ETB process with special focus on the development since 2014, benchmarking them against earlier systems with a large database of operational experience.

Oxidative desulfurization of model oil over Ta-Beta zeolite synthesized via structural reconstruction

As to metallosilicate zeolites, ions with larger size such as Ta⁵⁺ in the gels greatly retarded their crystallization during the hydrothermal synthesis, affording long-winded synthesis periods, up-limited framework-substituted metal contents, or even frustrated outcome. An efficient hydrothermal synthesis strategy for metallosilicate, in this case of Ta framework-substituted *BEA zeolite, via structural reconstruction was proposed to stride the gap. The Ta content in our developed Ta-Beta-Re-50 zeolite achieved up to 5.48 % (Si/Ta = 52), breaking through the limitation of Ta contents for conventional method (Si/Ta > 100). Additionally, this Ta-Beta-Re zeolite possessed nanosized crystals (20-40 nm) and short crystallization time (8 h), significantly improving space-time yields of practical zeolite production. Through spectroscopic study, it was confirmed that the existence of zeolite structural units intensively facilitated the formation of nucleation and crystal growth. This innovative Ta-Beta zeolite demonstrated high catalytic performances for oxidation desulfurization, far outperforming traditional fluoride-mediated Ta-Beta-F, which was ascribed to its excellent diffusion properties and incredible high isolated Ta contents. Additionally, the catalytic performance of Ta-Beta-Re could be regenerated after simple calcination and the deactivation may be caused by pore blocking of organics. This work provides a new method for rationally design and construction of metallosilicate materials with high activity for catalytic oxidation applications, which can bridge the conceptual and technical gap between periodic trends and zeolite material synthesis.

A Rotavirus Virus-Like Particle Confined Palladium Nanoreactor and Its Immobilization on Graphene Oxide for Catalysis

Abstract

In this work, a new viral protein cage based nanoreactor was successfully constructed via encapsulating Tween 80 stabilized palladium nanoparticles (NPs) into rotavirus capsid VP2 virus-like particles (i.e. Pd@VP2). The effects of stabilizers including CTAB, SDS, Tween 80 and PVP on controlling the particle size of Pd NPs were investigated. They were further immobilized on graphene oxide (i.e. Pd@VP2/GO) by a simple mixing method. Some characterizations including FT-IR and XPS were conducted to study adsorption mode of Pd@VP2 on GO sheets. Their catalytic performance was estimated in the reduction of 4-nitrophenol (4-NP). Results showed that Tween 80 stabilized Pd NPs with the molar ratio of Pd to Tween 80 at 1:0.1 possessed the smallest size and the best stability as well. They were encapsulated into viral protein cages (mean size 49 ± 0.26 nm) to assemble confined nanoreactors, most of which contained 1-2 Pd NPs (mean size 8.15 ± 0.26 nm). As-prepared Pd@VP2 indicated an enhanced activity (apparent reaction rate constant k _app  = (3.74 ± 0.10) × 10^-3 s^-1) for the reduction of 4-NP in comparison to non-confined Pd-Tween80 colloid (k _app  = (2.20 ± 0.06) × 10^-3 s^-1). It was logically due to confinement effects of Pd@VP2 including high dispersion of Pd NPs and high effective concentration of substrates in confined space. Pd@VP2 were further immobilized on GO surface through C-N bond. Pd@VP2/GO exhibited good reusability after recycling for four runs, confirming the strong anchoring effects of GO on Pd@VP2.

Graphic Abstract

Ethanol-to-butadiene: the reaction and its catalysts

Catalytic conversion of ethanol is a promising technology for producing sustainable butadiene. This paper reviews the reaction and its catalysts, and discusses the challenges their development faces.

Fundamental roles of ZnO and ZrO2 in the conversion of ethanol to 1,3-butadiene over ZnO–ZrO2/SiO2

ZnO and ZrO₂ sites in the ZnO–ZrO₂/SiO₂ catalyst act cooperatively to catalyze different steps of the conversion of ethanol to 1,3-butadiene.

Framework-confined Sn in Si-beta stabilizing ultra-small Pt nanoclusters as direct propane dehydrogenation catalysts with high selectivity and stability

Highly stable Pt/Sn-Si-beta catalysts were prepared via an improved post-synthesis method, exhibiting high catalytic activity, good selectivity and excellent stability for propane dehydrogenation to propene.

New trends in tailoring active sites in zeolite-based catalysts

This review discusses approaches for tailoring active sites in extra-large pore, nanocrystalline, and hierarchical zeolites and their performance in emerging catalytic applications.

Oxidative dehydrogenation of propane over Pt–Sn/Si-beta catalysts: key role of Pt–Sn interaction

Bimetallic Pt–Sn catalysts supported on dealuminated Si-beta zeolite were prepared via wet impregnation and the nanoscale close contact between Pt and Sn species in Pt–Sn/Si-beta was confirmed by electron microscopy analyses.