Catalysis Today最新文献

Lignin is the most abundant renewable resource composed of aromatic moieties in nature. The highlight aromatic characteristics of lignin renders it a sustainable feedstock for aromatic chemicals and naphthene fuels. Tungsten is a typical rare metal for the synthesis of non-noble metal catalysts which show potential in catalyzing lignin depolymerization/valorization. This review highlights the latest advances in the application of tungsten-based catalysts for the transformation of lignin into value-added chemicals and fuels. We focus on the synthesis and application of tungsten carbides, tungsten sulfide, tungsten phosphide, tungsten acids, and tungsten-based bimetallic catalysts on lignin conversion. Among them, tungsten carbides are extensively summarized. Perspectives for the future investigation on the lignin depolymerization are also presented.

Developing methods to transform industrial biomass waste into platform chemicals and materials is an important part of the EU circular bio-based economy. Thus, the present work focuses on the valorisation of crude sugarcane molasses (SCM) to 5-hydroxymethylfurfural (HMF) over starch-derived catalysts in water. A series of monofunctional catalysts having sulfonic, phosphate, or oxygen functionalities as Brönsted acid (BA) sites and a bifunctional catalyst containing phosphate groups as BA and SnO₂ as Lewis acid (LA) sites was prepared via one-pot hydrothermal carbonisation of starch. The effect of the varied active sites on these catalysts was tested in the cascade conversion of SCM to HMF in water using a microwave reactor. The results revealed that the maximum yield of HMF obtained from SCM depends solely on the chemistry of the catalyst's surface. It is independent of the catalyst's texture and is not proportional to the total acidity (A_tot). A promising HMF yield of around 30 % was obtained from crude SCM in pure water over sulfonated hydrochar catalyst containing –SO₃H, along with –OH and –COOH functionalities. The sulfonic groups were found to be the most selective towards fructose dehydration to HMF out of all of the BA sites tested here. On the other hand, introducing LA sites to the catalyst increased the conversion of glucose and selectivity to HMF compared to the monofunctional counterpart. However, the sugar conversion rate was lower over the bifunctional catalyst than that using sulfonated hydrochar. The catalytic system studied here was found to be suitable for high loadings of SCM. However, the best catalyst suffered a drop in activity after the first re-use. In general, obtaining high yields of HMF from SCM in water was hindered by a lack of effective isomerization of glucose to fructose and a high rate of side reactions producing humin, which were catalysed by impurities present in SCM. The transformation of SCM to HMF with sulfonated hydrochar occurred at a far slower rate than that of a solution of synthetic SCM (neat mixture of sugars) under similar conditions, which pointed to the negative effect of the impurities in the SCM matrix. Thus, it was shown that even though SCM is an interesting alternative feedstock for biorefineries, its purification prior to catalytic valorization might be necessary.

The effect of the CO₂:C₂H₆ feed ratio, the relative Lewis acidity of reducible and unreducible catalytically active metal oxide supports with and without Fe₃Ni₁ alloy nanoparticles on the activity, selectivity and stability for the CO₂-mediated oxidative dehydrogenation of ethane (CO₂-ODHE) is investigated. To circumvent the influence of the typically dissimilar textural properties of the supports in bulk form, overlayer oxide supports of V, Cr, Ga, Ti or Sm coated on a common γ-Al₂O₃ carrier were employed. Separately, (Ni_0.75Fe_0.25)Fe₂O₄ precursor nanoparticles were synthesized via a nonaqueous surfactant-free method, sonication-deposited onto supports and reduced in situ into an Fe₃Ni₁ alloy microstructure of bcc and fcc mixed phases captured with in situ XRD. When exposed to carbon dioxide at 255 °C, a selective re-oxidation of the bcc phase via CO₂ dissociation is observed, while the fcc phase stays stable and only partially re-oxidizes above 525 °C. Upon exposure to CO₂-ODHE conditions, the initial activity of the bare supports increases with increasing acid site strength, but this activity is rapidly lost in case of the strongly acidic supports. Comparison of the C₂H₄ and CO selectivity indicate direct dehydrogenation is preferred over the oxidative dehydrogenation pathway and is initially occurring in combination with some CO-forming routes, possibly the dry reforming of C₂H₆. This CO forming route is significant over the most acidic and reducible VO_x@Al₂O₃ support in the early stages of operation. The addition of the Fe₃Ni alloy increases the conversions of both C₂H₆ and CO₂ across all supports, with a notably stronger effect observed on CO₂ conversion especially over the highly acidic and reducible VO_x@Al₂O₃ and CrO_x@Al₂O₃. As a result, the CO selectivity is increased due to ethane dry reforming activity over the latter supports while CO₂-ODHE activity is observed over the supports with intermediate and weak acid sites.

The use of water solutions of surfactants as the reaction medium to carry out cross-coupling reactions on water-insoluble materials is a topic of great interest in sustainable chemistry. Reactions are efficient, fast, compatible with mild or no heating, and require lower catalyst loading with respect to homogeneous phase ones performed in organic solvents. The use of supported, cheap, and widely available catalysts within the context of chemistry in water offers additional advantages: ease of removal, recovery, and recycling of the catalyst as well as a further reduction of costs and environmental impact. We here show that in the presence of a suitable surfactant, palladium-on-carbon – one of the simplest and cheapest supported palladium catalysts – is an exceedingly efficient catalyst to attain ligand-free Suzuki-Miyaura coupling of aryls and heteroaryls in water under standard laboratory atmosphere at Pd loading as low as 400 ppm.

The production of Sustainable Aviation Fuel (SAF) utilizing used cooking oil (UCO) as a renewable bio-waste resource holds immense potential for promoting sustainability in the aviation sector. In this study, SAF synthesis via hydrodeoxygenation of pretreated UCO over Ni-Mo/alumina-silica catalysts followed up hydroisomerization of deoxygenated oil has been investigated in a fixed-bed reactor. The effect of Al₂O₃/SiO₂ ratio on the physico-chemical properties of Al₂O₃-SiO₂ support and on the overall hydrodeoxygenation performance of the Ni-Mo catalyst supported on Al₂O₃-SiO₂ has been investigated. NiMo catalyst supported on Al2O₃-SiO₂ in a 70:30 ratio achieved 86.69 % UCO conversion during the hydrodeoxygenation step and exhibited 74.79 % jet range hydrocarbon fuel selectivity under mild conditions (350°C, 1.1 h⁻¹ WHSV, 6 MPa, H₂/oil (v/v): 400). The catalyst activity remained stable for >100 hours highlighting its good stability under the experimental conditions investigated. This work demonstrates the potential of tailor-made supported catalysts for highly selective single-step conversion of UCO into jet-range hydrocarbons, offering a significant step towards the production of sustainable aviation fuels.

The development of effective catalysts for the hydrogenation of CO₂ to methanol is a crucial step in enhancing the efficiency of the green synthesis of chemicals and fuels. Herein, we investigated the use of transition metal carbides in CO₂ hydrogenation at low temperatures (160–200 °C). Mo₂C-based catalysts synthesized in a vertical fixed-bed reactor exhibited 3–4 times higher activity than the catalyst synthesized in a horizontal reactor from open bulk in a boat vessel. This difference in activity is likely due to the lower surface area of the catalyst obtained by the latter method, as well as the non-uniform and incomplete formation of the Mo₂C phase. The study also demonstrates that unpromoted Mo₂C produced more methane and higher alkanes, indicating the potential of Mo₂C in the CO₂ hydrogenation to hydrocarbons. Additionally, Cu/Mo₂C was 3.75 times more active than unpromoted Mo₂C at 160 °C, with higher selectivity towards methanol. CH₃OH was the predominant product over Cu/Mo₂C in the temperature range of 160–200 °C. The experiments aimed to elucidate the reaction mechanism over Cu/Mo₂C catalyst in CO₂ hydrogenation to identify primary and secondary products.

The conversion of carbon dioxide (CO₂) through non-thermal plasma catalysis has received significant attention as a promising approach to address both environmental and energy challenges. This review paper offers a comprehensive overview of recent advancements in CO₂ conversion utilizing non-thermal plasma (NTP), focusing on its potential to achieve efficient and selective transformations of CO₂ into valuable products, such as fuels and chemicals, at moderate reaction conditions. The unique ability of NTP to activate CO₂ at ambient room temperature and atmospheric pressure offers a promising pathway to mitigate the greenhouse effect and reduce dependency on fossil fuels. We highlight the utilization of catalysts in combination with dielectric barrier discharge (DBD) plasma reactor, showcasing encouraging results in enhancing product selectivity and overall CO₂ conversion. Nevertheless, challenges associated with the conversion of CO₂ into specific oxygenates, like methanol, are also discussed. The maximum methanol selectivity reported from recent studies was ∼86 % from CO₂ hydrogenation reaction with DBD reactor. This review provides valuable insights for researchers working on sustainable CO₂ utilization strategies and aids in guiding future investigations in this burgeoning field.

VOx/TiO₂ catalysts with various theorical monolayer values have been prepared and used to study, for the first time, the effect of vanadium loading in the selective oxidation of glucose to formic acid. Monomeric or isolated vanadia species dominate at low loadings, evolving into polymeric chains at higher concentrations, while crystalline V₂O₅ is observed at loadings over the theoretical monolayer value. Their characterization by XRD, BET, ICP, DRIFTS, Raman, UV–vis, H₂-TPR and NH₃-TPD reveal distinct physicochemical characteristics influenced by the formed vanadia species, impacting sample acidity, reducibility, and catalytic activity.

All catalysts exhibit significant activity, forming formic acid as the main product in the liquid phase and reaching a peak formic acid yield of 42 %. Post-reaction analysis reveals that the leaching-prone crystalline V₂O₅ compromises catalyst stability while isolated vanadia species demonstrate superior catalytic activity and leaching resistance. The findings of this study provide a strong basis for the development of a heterogeneous vanadia catalyst with improved interaction with the support.

The activity of copper oxide under irradiation is majorly attributed to the shape and purity of the synthesized materials. To achieve these characteristics, magnetron sputtering was introduced as an efficient technique. Although the stability of these materials is low in photoelectrochemical water splitting, they can be reasonably stable in CO₂ reduction. However, their activity is low due to the high charge recombination rate. Designing heterojunction architectures can be an efficient approach to achieving high activity in CO₂ reduction by increasing the lifetime of photogenerated excitons and decreasing the charge recombination rate. This study presents Cu_xO photocatalysts as promising candidates for creating the heterojunction structure with TiO₂. The thin copper oxide films were obtained with magnetron sputtering and successive ionic layer adsorption and reaction (SILAR) methods. The pristine and heterojunction bilayer films were profoundly investigated. The oxidation states of copper, crystalline form, and morphology of copper oxide and their heterojunction films were studied thoroughly. Furthermore, the photogenerated charges’ fate and direction in the heterojunction bilayer films were studied with the measured surface photovoltage (SPV), employing a Kelvin probe. The SPV and ToF-SIMS analysis confirmed the creation of a junction between copper oxide and titanium dioxide. The photo(electro)catalytic activity of the synthesized materials was studied in solar water splitting and CO₂ reduction. Herein, we additionally report the generation of oxygen during the CO₂ reduction. Moreover, the materials obtained using the SILAR method showed considerably higher activity than those obtained using magnetron sputtering.

Most practical applications of photocatalysts will involve coatings on an inert support; here we have examined how copper doping of spin coated porous TiO₂ films affects their physical characteristics and photocatalytic activity. The photocatalytic degradation of stearic acid was used as a measure of photocatalytic activity for catalysts spin coated from a sol-gel onto glass with 0, 0.1, 0.5, 1, 2.5 and 5 wt% copper introduced into the catalyst lattice before gelation. The effects of spin coating speed on film thickness, structure and band gap were studied and the nature of the copper incorporated into the films examined with XPS and XANES measurements. Increased spin coating speeds reduces the thickness of the deposited films from ∼ 50 μm to ∼ 20 μm until a spin speed of ∼ 3000 rpm at which point non-Newtonian behaviour of the gels prevents further reductions in film thickness. A larger effect on film thickness is the presence of the added copper nitrate which results in thinner films. After calcining, XANES shows the bulk of the copper to be in a Cu(II) state but at the surface of the thinnest, most active films XPS shows only Cu(I). Photocatalytic activity is much more strongly affected by the presence of the copper than the thickness of the films with 0.1 wt% Cu catalysts as much as 10 times more active than the undoped catalysts. Increasing the copper content, however, reduces activity until at ∼ 5 wt% activity is lower than for the pure TiO₂ films.