Ex Situ and Operando Studies on the Role of Copper in Cu-Promoted SiO2–MgO Catalysts for the Lebedev Ethanol-to-Butadiene Process

The concept of active site in heterogeneous catalysis

Catalysis is at the core of chemistry and has been essential to make all the goods surrounding us, including fuels, coatings, plastics and other functional materials. In the near future, catalysis will also be an essential tool in making the shift from a fossil-fuel-based to a more renewable and circular society. To make this reality, we have to better understand the fundamental concept of the active site in catalysis. Here, we discuss the physical meaning - and deduce the validity and, therefore, usefulness - of some common approaches in heterogeneous catalysis, such as linking catalyst activity to a 'turnover frequency' and explaining catalytic performance in terms of 'structure sensitivity' or 'structure insensitivity'. Catalytic concepts from the fields of enzymatic and homogeneous catalysis are compared, ultimately realizing that the struggle that one encounters in defining the active site in most solid catalysts is likely the one we must overcome to reach our end goal: tailoring the precise functioning of the active sites with respect to many different parameters to satisfy our ever-growing needs. This article ends with an outlook of what may become feasible within the not-too-distant future with modern experimental and theoretical tools at hand.

A DFT study of the aldol condensation reaction in the processing of ethanol to 1,3-butadiene on a MgO/SiO2 surface

The ETB process on different sites of MgO/SiO2.

Direct SVUV-PIMS identification of unstable oxygenated intermediates in ethanol to butadiene reaction

SVUV-PIMS was employed for the identification of unstable intermediates in the ethanol to butadiene reaction over a MgO–SiO2 catalyst. Supposed intermediate acetaldol and unexpected intermediate ketene were experimentally observed.

Bioethanol Upgrading to Renewable Monomers Using Hierarchical Zeolites: Catalyst Preparation, Characterization, and Catalytic Studies

Bioethanol is one of the most promising renewable resources for the production of important monomers. To date, there have been various processes proposed for bioethanol conversion to renewable monomers. In this review, the catalytic bioethanol upgrading to various types of monomers using hierarchical zeolites as catalysts is illustrated, including the recent design and preparation of hierarchical zeolites for these catalytic processes. The characterizations of catalysts including textural properties, pore architectures, acidic properties, and active species are also exemplified. Moreover, the catalytic studies with various processes of monomer production from bioethanol including bioethanol dehydration, bioethanol to hydrocarbons, and bioethanol to butadiene are revealed in terms of catalytic activities and mechanistic studies. In addition, the future perspectives of these catalytic circumstances are proposed in both economic and sustainable development contexts.

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.

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.

Design and synthesis of a novel coumarin-based framework as a potential chemomarker of a neurotoxic insecticide, azamethiphos

A coumarin based receptor has been synthesised and its organic nanoparticles were prepared. Further, these nanoparticles were explored as a chemosensor for copper(ii) ions and azamethiphos.

Ethynylation of Formaldehyde over CuO/SiO2 Catalysts Modified by Mg Species: Effects of the Existential States of Mg Species

The highly effective catalytic synthesis of 1,4-butynediol (BD) from the Reppe process is a fascinating technology in modern chemical industry. In this work, we reported the effects of the existential states of Mg species in the CuO/silica-magnesia catalysts for the ethynylation of formaldehyde in a simulative slurry reactor. The physichemical properties of the supports and the corresponding catalysts were extensively characterized by various techniques. The experimental results indicated that the introduced Mg species in the form of MgO particles, MgO microcrystals, or Si-O-Mg structures effectively resulted in an abundance of medium-strong basic sites, which can synergize with the active Cu⁺ species, facilitate the activation of acetylene, and improve the ethynylation activity. For the CuO/MgO-SiO₂ catalyst, the existence of Si-O-Mg structures strengthened the Cu–support interaction, which were beneficial to improving the dispersion and the valence stability of the active Cu⁺ species. The highly dispersed Cu⁺ species, its stable valence state, and the abundant medium-strong basic sites enhanced the synergistic effect significantly, leading to the superior activity and stability of CuO/MgO-SiO₂. The insights into the role of the existential states of Mg species and the revelation of the synergistic effect between active Cu⁺ species and basic sites can provide theoretic guidance for future rational design of catalysts for the ethynylation reation.

A hybrid composite of hydroxyapatite and Ca-Al layered double hydroxide supported Au nanoparticles for highly efficient base-free aerobic oxidation of glucose

In this work, a new hybrid composite of hydroxyapatite and Ca-Al layered double hydroxide (HAP-LDH) was successfully assembled via an in situ growth route, by which large quantities of small needle-like HAP crystals in situ grew over the lateral surface of large platelet-like CaAl-LDH particles, and applied to immobilize Au nanoparticles for base-free aerobic glucose oxidation in water to produce gluconic acid using molecular oxygen. A combination of characterization techniques and catalytic experiments revealed that the activity of supported Au catalysts was strongly associated with the composition of supports, and the hybrid HAP-LDH supported one with a Au loading amount of about 0.2 wt% delivered a high gluconic acid yield of >98% under optimal reaction conditions, along with a quite high turnover frequency value of ∼20 225 h-1. High efficiency of the as-formed Au/HAP-LDH was mainly ascribed to cooperation between favorable surface Au species (Au0/Auδ+) and abundant basic sites. Furthermore, the present catalyst also presented good structural stability, because of the novel hybrid three-dimensional nano/microstructure of the HAP-LDH composite support facilitating the stabilization of active Au species and components of the support. The present synthesis strategy of employing a hybrid composite support provides a new way to design stable and high-performance supported metal nanocatalysts for a variety of advanced heterogeneous catalytic processes.

Synthesis of 1,3-Butadiene and Its 2-Substituted Monomers for Synthetic Rubbers

Synthetic rubbers fabricated from 1,3-butadiene (BD) and its substituted monomers have been extensively used in tires, toughened plastics, and many other products owing to the easy polymerization/copolymerization of these monomers and the high stability of the resulting material in manufacturing operations and large-scale productions. The need for synthetic rubbers with increased environmental friendliness or endurance in harsh environments has motivated remarkable progress in the synthesis of BD and its substituted monomers in recent years. We review these developments with an emphasis on the reactive routes, the products, and the synthetic strategies with a scaling potential. We present reagents that are primarily from bio-derivatives, including ethanol, C4 alcohols, unsaturated alcohols, and tetrahydrofuran; the major products of BD and isoprene; and the by-products, activities, and selectivity of the reaction. Different catalyst systems are also compared. Further, substituted monomers with rigid, polar, or sterically repulsive groups, the purpose of which is to enhance thermal, mechanical, and interface properties, are also exhaustively reviewed. The synthetic strategies using BD and its substituted monomers have great potential to satisfy the increasing demand for better-performing synthetic rubbers at the laboratory scale; the laboratory-scale results are promising, but a big gap still exists between current progress and large scalability.

Base-free hydrogen generation from formaldehyde and water catalyzed by copper nanoparticles embedded on carbon sheets

Base-free hydrogen generation through complete dehydrogenation from formaldehyde and water catalyzed by Cu nanoparticles embedded on carbon sheets.

Enhancement of Copper Catalyst Stability for Catalytic Ozonation in Water Treatment Using ALD Overcoating

Atomic layer deposition (ALD) of alumina overcoating can significantly enhance the stability of copper oxide-based catalysts for catalytic ozonation of organic compounds in advanced water/wastewater treatment. The catalyst leaching was reduced by about 90% while high (up to 98%) activity was demonstrated in terms of total organic carbon (TOC) removal. Synchrotron X-ray absorption spectroscopy results indicated that the Al₂O₃ protecting layer passivated the under-coordinated copper sites, which were likely to be responsible for leaching.

A DFT study on the aldol condensation reaction on MgO in the process of ethanol to 1,3-butadiene: understanding the structure–activity relationship

The mechanism of aldol condensation on MgO surfaces with different structures was investigated to illustrate the structure–activity relationship.

Effect of SiO2 support properties on the performance of Cu–SiO2 catalysts for the hydrogenation of levulinic acid to gamma valerolactone using formic acid as a hydrogen source

Vapor phase catalytic transfer hydrogenation of levulinic acid with formic acid was carried out over Cu–SiO₂ catalysts having different physicochemical properties.

Direct synthesis of isobutyraldehyde from methanol and ethanol on Cu–Mg/Ti-SBA-15 catalysts: the role of Ti

An increase in the Ti content significantly improves catalyst durability due to its effect on Cu dispersion and the basicity of the catalyst.