Gas-phase epoxidation of propylene in the presence of H2 and O2 over small gold ensembles in uncalcined TS-1

Nanoparticles as an antidote for poisoned gold single-atom catalysts in sustainable propylene epoxidation

The development of sustainable and anti-poisoning single-atom catalysts (SACs) is essential for advancing their research from laboratory to industry. Here, we present a proof-of-concept study on the poisoning of Au SACs, and the antidote of Au nanoparticles (NPs), with trace addition shown to reinforce and sustain propylene epoxidation. Multiple characterizations, kinetics investigations, and multiscale simulations reveal that Au SACs display remarkable epoxidation activity at a low propylene coverage, but become poisoned at higher coverages. Interestingly, Au NPs can synergistically cooperate with Au SACs by providing distinct active sites required for H2/O2 and C3H6 activations, as well as hydroperoxyl radical to restore poisoned SACs. The difference in reaction order between C3H6 and H2 (nC3H6-nH2) is identified as the descriptor for establishing the volcano curves, which can be fine-tuned by the intimacy and composition of SACs and NPs to achieve a rate-matching scenario for the formation, transfer, and consumption of hydroperoxyl. Consequently, only trace addition of Au NPs antidote (0.3% ratio of SACs) stimulates significant improvements in propylene oxide formation rate, selectivity, and H2 efficiency compared to SACs alone, offering a 56-fold, 3-fold, and 22-fold increase, respectively, whose performances can be maintained for 150 h.

Influence of the Support on Propene Oxidation over Gold Catalysts

The epoxidation of propene without forming a substantial amount of byproducts is one of the holy grails of catalysis. Supported Cu, Ag and Au catalysts are studied for this reaction and the activity of the supported metals is generally well understood. On the contrary, limited information is available on the influence of the support on the epoxide selectivity. The reaction of propene with equal amounts of hydrogen and oxygen was tested over gold nanoparticles deposited onto CeO2, TiO2, WO3, γ-Al2O3, SiO2, TiO2-SiO2 and titanosilicate-1. Several metal oxide supports caused further conversion of the synthesized propene oxide. Strongly acidic supports, such as WO3 and titanosilicate-1, catalyzed the isomerization of propene oxide towards propanal and acetone. Key factors for achieving high PO selectivity are having inert or neutralized surface sites, a low specific surface and/or a low density of surface -OH groups. This work provides insights and practical guidelines to which metal oxide support properties lead to which products in the reaction of propene in the presence of oxygen and hydrogen over supported gold catalysts.

The Lord of the Chemical Rings: Catalytic Synthesis of Important Industrial Epoxide Compounds

The epoxidized group, also known as the oxirane group, can be considered as one of the most crucial rings in chemistry. Due to the high ring strain and the polarization of the C–O bond in this three-membered ring, several reactions can be carried out. One can see such a functional group as a crucial intermediate in fuels, polymers, materials, fine chemistry, etc. Literature covering the topic of epoxidation, including the catalytic aspect, is vast. No review articles have been written on the catalytic synthesis of short size, intermediate and macro-molecules to the best of our knowledge. To fill this gap, this manuscript reviews the main catalytic findings for the production of ethylene and propylene oxides, epichlorohydrin and epoxidized vegetable oil. We have selected these three epoxidized molecules because they are the most studied and produced. The following catalytic systems will be considered: homogeneous, heterogeneous and enzymatic catalysis.

Direct Gas-Phase Oxidation of Propylene to Acetone in the Presence of H2 and O2 over Au/TS-1 Catalyst

A novel process for the preparation of acetone is reported by gas-phase oxidation of propylene in the presence of H2 and O2 with Au supported TS-1 catalyst (Au/TS-1). By elevating the reaction temperature to 280°C, Au/TS-1 catalyzes 11.6% propylene generating acetone with 70.6% selectivity, and 8.2% acetone in onepass yield. Acetone is originated from propylene oxide isomerization, which is mainly attributed to the surface of the Lewis base and high reaction temperature. Furthermore, small Au nanoparticle size promotes the reaction.

Advances in Designing Au Nanoparticles for Catalytic Epoxidation of Propylene with H2 and O2

Au nanoparticles, which can be used in various industrial and environmental applications, have drawn substantial research interest. In this review, a comprehensive background and some insights are provided regarding recent studies concerning the use of Au nanoparticles for catalytic propylene epoxidation with H2 and O2. Over the last two decades, substantial progress has been made toward the efficient production of propylene oxide (PO); this includes the design of highly dispersed Au catalysts on Ti-modified mesoporous silica supports, the optimization of catalytic epoxidation, and the determination of the mechanisms and reaction pathways of epoxidation. Particularly, the critical roles of catalyst synthesis, the types of material support, Au nanoparticle sizes, and the dispersion amounts of Au nanoparticles are emphasized in this review. In future studies, novel, practical, robust, and highly PO-selective Au nanoparticle catalyst systems are expected to be continually designed for the enhanced catalytic epoxidation of propylene.

Engineering of Transition Metal Catalysts Confined in Zeolites

Transition metal-zeolite composites are versatile catalytic materials for a wide range of industrial and lab-scale processes. Significant advances in fabrication and characterization of well-defined metal centers confined in zeolite matrixes have greatly expanded the library of available materials and, accordingly, their catalytic utility. In this review, we summarize recent developments in the field from the perspective of materials chemistry, focusing on synthesis, postsynthesis modification, (operando) spectroscopy characterization, and computational modeling of transition metal-zeolite catalysts.

Thermal stability of TPA template and size-dependent selectivity of uncalcined TS-1 supported Au catalyst for propene epoxidation with H2 and O2

An Au/TS-1-B catalyst, whose internal TPA template is stable below 350 °C, shows volcano-shaped activity with reaction temperature and reaches a noteworthy PO formation rate (220 g_PO h⁻¹ kg_Cat⁻¹) at 260 °C. Moreover, intrinsic size-dependent selectivity is also studied.

Gold supported on Ti incorporated MCM-36 as efficient catalysts in propylene epoxidation with H2and O2

Au NPs supported on titanosilicate pillared MCM-36 with 2 nm mesopores were prepared. The influence of the Ti coordination environment on the particle size of anchored Au NPs and their catalytic performance in propylene epoxidation with H₂/O₂mixtures were investigated.