Catalysts — Open Access Catalysis Journal

This research introduces a completely new environmental benign synthesis route for obtaining two kinds of inter-mediate and high temperature CO2 sorbents, Mg-Al layered double hydroxide (LDH) and Li4SiO4, from vermiculite. The mineral vermiculite was leached with acid, from which the obtained SiO2 was used for the synthesis of Li4SiO4 and the leaching waste water was used for the synthesis of Mg-Al LDH. Therefore, no waste was produced during the whole process. Both Li4SiO4 and Mg-Al LDH sorbents were carefully characterized using XRD, SEM, and BET analyses. The CO2 capturing performance of these two sorbents was comprehensively evaluated. The influence of the Li/Si ratio, calcination temperature, calcination time, and sorption temperature on the CO2 sorption capacity of Li4SiO4, and the sorption temperature on the CO2 sorption capacity of LDH, were investigated. The optimal leaching acid concentration for vermiculite and the CO2 sorption/desorption cycling performance of both the Li4SiO4 and Mg-Al LDH sorbents were determined. In sum, this demonstrated a unique and environment-friendly scheme for obtaining two CO2 sorbents from cheap raw materials, and this idea is applicable to the efficient utilization of other minerals. Full article

Ni–Ce–Zr mixed oxides were prepared through one-pot hydrolysis of mixed metal nitrates with ammonium carbonate for CO₂ methanation. The effects of Ce/Zr molar ratio and Ni content on catalysts’ physical and chemical properties, reduction degree of Ni²⁺, and catalytic properties were systematically investigated. The results showed that Zr could lower metallic Ni particle sizes and alter interaction between Ni and supports, resulting in enhancements in the catalytic activity for CO₂ methanation. The Ni–Ce–Zr catalyst containing 40 wt % Ni and Ce/Zr molar ratio of 9:1 exhibited the optimal catalytic properties, with 96.2% CO₂ conversion and almost 100% CH₄ selectivity at a low temperature of 275 °C. During the tested period of 500 h, CO₂ conversion and CH₄ selectivity over Ni–Ce–Zr catalyst kept constant under 300 °C. Full article

Six Co-Rh/Fe₃O₄ catalysts with different cobalt loadings were prepared by the co-precipitation of RhCl₃, Co(NO₃)₂, and Fe(NO₃)₃ using Na₂CO₃ as the precipitant. These catalysts were tested for dicyclopentadiene (DCPD) hydroformylation to monoformyltricyclodecenes (MFTD) and diformyltricyclodecanes (DFTD). The results showed that the MFTD formation rate increased with increasing cobalt loading, whereas the DFTD formation rate initially increased and then decreased when the cobalt loading was greater than twice that of Rh. The DFTD selectivity was only 21.3% when monometallic Rh/Fe₃O₄ was used as the catalyst. In contrast, the selectivity was 90.6% at a similar DCPD conversion when the bimetallic 4Co-2Rh/Fe₃O₄ catalyst was employed. These catalysts were characterized by temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and thermogravimetric and differential thermal analyses (TG-DTA). The results obtained by these complimentary characterization techniques indicated that adding cobalt to the Rh/Fe₃O₄ catalyst enhanced the Rh reducibility and dispersion; the Rh reducibility was easily altered, and increasing the cobalt loading improved the Rh dispersion. It was concluded that the enhanced catalytic performance with increasing cobalt loading might be due to the formation of a more reactive Rh species with a different Rh–phosphine interaction strength on the catalyst surface. Full article

Two types of heterometallic (Fe(III),Na) silsesquioxanes—[Ph₅Si₅O₁₀]₂[Ph₁₀Si₁₀O₂₁]Fe₆(O^2‒)₂Na₇(H₃O⁺)(MeOH)₂(MeCN)_4.5.1.25(MeCN), I, and [Ph₅Si₅O₁₀]₂[Ph₄Si₄O₈]₂Fe₆Na₆(O^2‒)₃(MeCN)_8.5(H₂O)_8.44, II—were obtained and characterized. X-ray studies established distinctive structures of both products, with pair of Fe(III)-O-based triangles surrounded by siloxanolate ligands, giving fascinating cage architectures. Complex II proved to be catalytically active in the formation of amides from alcohols and amines, and thus becoming a rare example of metallasilsesquioxanes performing homogeneous catalysis. Benzene, cyclohexane, and other alkanes, as well as alcohols, can be oxidized in acetonitrile solution to phenol—the corresponding alkyl hydroperoxides and ketones, respectively—by hydrogen peroxide in air in the presence of catalytic amounts of complex II and trifluoroacetic acid. Thus, the cyclohexane oxidation at 20 °C gave oxygenates in very high yield of alkanes (48% based on alkane). The kinetic behaviour of the system indicates that the mechanism includes the formation of hydroxyl radicals generated from hydrogen peroxide in its interaction with di-iron species. The latter are formed via monomerization of starting hexairon complex with further dimerization of the monomers. Full article

Caprolactam-based ionic liquids show many advantages, such as the lower toxicity, lower cost, and a simple preparation process. In this work, caprolactam-based ionic liquids were prepared and adopted as catalysts for the transesterification of Jatropha oil with methanol. The results demonstrated that the SO₃H-functional caprolactam‐based ionic liquids have higher catalytic activity than those of the caprolactam-based ionic liquids without sulfonic group or the SO₃H-functional pyridine-based ionic liquids, attributed to their stronger Brønsted acidity. By optimizing the reaction parameter, the biodiesel yield catalyzed by 1-(4-sulfonic group) butylcaprolactamium hydrogen sulfate ([HSO₃-bCPL][HSO₄]) could reach above 95% at 140 °C for 3 h. Furthermore, the ionic liquid had a good reusability. Full article

Photocatalytic nanomaterials such as TiO₂ are receiving a great deal of attention owing to their potential applications in environmental remediation. Nonetheless, the low efficiency of this class of materials in the visible range has, so far, hampered their large-scale application. The increasing demand for highly efficient, visible-light-active photocatalysts can be addressed by hybrid nanostructured materials in which two or more units, each characterised by peculiar physical properties, surface chemistry and morphology, are combined together into a single nano-object with unprecedented chemical–physical properties. The present review intends to focus on hybrid nanomaterials, based on TiO₂ nanoparticles able to perform visible-light-driven photocatalytic processes for environmental applications. We give a brief overview of the synthetic approaches recently proposed in the literature to synthesise hybrid nanocrystals and discuss the potential applications of such nanostructures in water remediation, abatement of atmospheric pollutants (including NO_x and volatile organic compounds (VOCs)) and their use in self-cleaning surfaces. Full article

A facile and effective growing strategy of graphite-like carbon nitride quantum dots (CNQDs) modified on ZnO nanowire array composite electrodes has been successfully designed and prepared for the first time. The remarkable quantum enhanced properties were carefully studied by means of scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS), UV-vis diffuse reflectance, PEC performance, and photocatalytic hydrogen production, and the results were in good agreement. Fivefold enhanced photoelectrochemical performances of this novel hierarchical hetero-array prepared in this paper compared with pure ZnO nanowire arrays were obtained under UV-light. The effect was attributed to the remarkable charge separation between CNQDs and ZnO nanowire arrays. Additional investigations revealed that the particular structure of CNQDs/ZnO composites contributed to the separation of a photon-generation carrier and an enhanced photoelectric current. Moreover, the absorption edge of CNQD-modified ZnO nanowire arrays was slightly broadened, and the diameter was reduced as well. The photoelectrochemistry hydrogen evolution splitting water using simulated solar irradiation exhibited the foreground of a possible application of a mechanism of photoelectrochemistry hydrogen evolution over CNQDs/ZnO composite electrodes. Full article

This study assessed 3D WO₃–TiO₂ nanoflowers (WTNF) synthesized by a combined hydrothermal–ultrasonication–impregnation method for their applicability to the treatment of aromatic volatile compounds under visible-light illumination. The scanning electron microscopy exhibited the formation of 3D structures in the prepared WTNF samples. The X-ray diffraction patterns and energy dispersive X-ray results indicated a successful incorporation of WO₃ into TNF structures. The UV-visible spectroscopy showed that the prepared WTNF samples can be functioned under visible light irradiation. The output-to-input concentration ratios of toluene and o-xylene with WTNF samples were lower than those of TiO₂ nanoflowers. These findings were illustrated on the basis of charge separation ability, adsorption capability, and light absorption of the sample photocatalysts. The input-to-output concentration ratios of the target chemicals were lowest for 10 M NaOH and highest for 5 M NaOH. The photocatalytic degradation efficiencies of WTNF sample photocatalysts increased with increasing WO₃ content from 0.1% to 1.0%, and dropped gradually with increasing WO₃ content further to 4.0%. Light-emitting-diodes (LEDs) are a more highly energy-efficient light source compared to a conventional lamp for the photocatalytic degradation of toluene and o-xylene, although the photocatalytic activity is higher for the conventional lamp. Full article

Several CeO₂ and CuO-CeO₂ catalysts were prepared using different methods, i.e., a homogeneous precipitation with urea, a nanocasting route using CMK-3 carbon as a hard template and a sol–gel process using Poly(methyl methacrylate) (PMMA) polymer as a soft template, and tested in the total oxidation of propane. The catalysts were characterized by a number of physicochemical techniques (XRD, N₂ adsorption, TPR, XPS, Raman spectroscopy) showing distinct characteristics. For each series, Cu-Ce-O catalysts with low Cu-loadings (5 wt % CuO) showed the highest activity, higher than those samples either without copper or with high Cu-loading (13 wt % CuO). The incorporation of copper leads to an increase of the concentration of bulk defects but if the Cu-loading is too high the surface area drastically falls. The highest activity in the total oxidation of propane was achieved by Cu-containing ceria catalysts synthesized using a polymer as a template, as this method yields high surface area materials. The surface area and the number of bulk/sub-surface defects of the ceria seem to be the main properties determining the catalytic activity. Full article

Eco-compatible activation methods in Suzuki–Miyaura cross-coupling reactions offer challenging opportunities for the design of clean and efficient synthetic processes. The main enabling technologies described in the literature are microwaves, ultrasound, grinding (mechanochemistry) and light. These methods can be performed in water or other green solvents with phase-transfer catalysis or even in solventless conditions. In this review, the authors will summarize the progress in this field mainly from 2010 up to the present day. Full article

Palladacycles are highly efficient precatalysts in cross-coupling reactions whose immobilization on carbonaceous materials has been hardly studied. Herein, we report a detailed study on the synthesis and characterization of new oxime palladacycle-graphene oxide non-covalent materials along with their catalytic activity in the Suzuki–Miyaura reaction. Catalyst 1-GO, which has been fully characterized by ICP, XPS, TGA, and UV-Vis analyses has been demonstrated to be an efficient catalyst for the Suzuki–Miyaura coupling between aryl bromides and arylboronic acids using very low catalyst loadings (0.002 mol % of Pd) at room temperature under aqueous conditions. Full article

The conversion of alcohols towards aldehydes in the presence of catalysts by non-oxidative dehydrogenation requires special importance from the perspective of green chemistry. Sodium (Na) super ionic conductor (NASICON)-type hydrogen titanium phosphate sulfate (HTPS; H_1−xTi₂(PO₄)_3−x(SO₄)_x, x = 0.5–1) catalysts were synthesized by the sol-gel method, characterized by N₂ gas sorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), NH₃ temperature-programmed desorption (NH₃-TPD), ultraviolet–visible (UV-VIS) spectroscopy, and their catalytic properties were studied for the non-oxidative dehydrogenation of methanol and ethanol. The ethanol is more reactive than methanol, with the conversion for ethanol exceeding 95% as compared to methanol, where the conversion has a maximum value at 55%. The selectivity to formaldehyde is almost 100% in methanol conversion, while the selectivity to acetaldehyde decreases from 56% to 43% in ethanol conversion, when the reaction temperature is increased from 250 to 400 °C. Full article

Thermomyceslanouginosalipase has been used to develop improved methods for carrier-free immobilization, the Cross-Linked Enzyme Aggregates (CLEAs), for its application in detergent products. An activator step has been introduced to the CLEAs preparation process with the addition of Tween 80 as activator molecule, in order to obtain a higher number of the individual lipase molecules in the ”open lid” conformation prior to the cross-linking step. A terminator step has been introduced to quench the cross-linking reaction at an optimal time by treatment with an amine buffer in order to obtain smaller and more homogenous cross-linked particles. This improved immobilization method has been compared to a commercially available enzyme and has been shown to be made up of smaller and more homogenous particles with an average diameter of 1.85 ± 0.28 µm which are 129.7% more active than the free enzyme. The CLEAs produced show improved features for commercial applications such as an improved wash performance comparable with the free enzyme, improved stability to proteolysis and a higher activity after long-term storage. Full article

2,5-Bis-(hydroxymethyl)furan (BHMF) is an important biomass-based platform chemical that can be derived from the hydrogenation of biomass-based 5-hydroxymethylfurfural (HMF). In this paper, the formation of BHMF from HMF via the catalytic transfer hydrogenation (CTH) process, using isopropanol as the hydrogen source and Ru/Co₃O₄ as the catalyst, was studied. The results revealed that the Ru/Co₃O₄ catalyst displayed a high catalytic efficiency, and that a BHMF yield of up to 82% was obtained at 190 °C in 6 h. Moreover, it was found that the recovered Ru/Co₃O₄ exhibited a similar catalytic activity to the pristine Ru/Co₃O₄ catalyst. These results supported the conclusion that the present CTH process is an attractive green route for the synthesis of BHMF from biomass-based HMF. Full article

The investigation of the water oxidation mechanism on photocatalytic semiconductor surfaces has gained much attention for its potential to unlock the technological limitations of producing H₂ from carbon-free sources, i.e., H₂O. This review seeks to highlight the available scientific and fundamental understanding towards the water oxidation mechanism on ZnO surfaces, as well as present a summary on the modification strategies carried out to increase the photocatalytic response of ZnO. Full article

The synthesis of a new class of epoxide derivatives from prochiral vinylidene bisphosphonate (VBP) precursors is reported using hydrogen peroxide as the terminal oxidant. The reaction is carried out using a series of possible organic activators having a basic character, with the best results being observed using quinine and sparteine. These activators not only provide from good to excellent epoxide yields with a large variety of VBPs, but also interesting enantioselectivities in the 67%–96% ee range, at least in the case of the Ph and m-MeO–Ph VBP derivatives, opening the way to a number of chiral anti-osteoporosis potentially active pharmaceutical ingredients. Full article

Microwave-assisted organic synthesis (MAOS) provides a novel and efficient means of achieving heat organic reactions. Nevertheless, the potential arcing phenomena via microwave (MW) interaction with solid metal catalysts has limited its use by organic chemists. As arcing phenomena are now better understood, new applications of Pd/C-catalyzed reactions under MW dielectric heating are now possible. In this review, the state of the art, benefits, and challenges of coupling MW heating with heterogeneous Pd/C catalysis are discussed to inform organic chemists about their use with one of the most popular heterogeneous catalysts. Full article

Development of sustainable energy technologies and reduction of carbon dioxide in the atmosphere are the two effective strategies in dealing with current environmental issues. Herein we report a Dual Function Material (DFM) consisting of supported sodium carbonate in intimate contact with dispersed Ru as a promising catalytic solution for combining both approaches. The Ru-Na₂CO₃ DFM deposited on Al₂O₃ captures CO₂ from a flue gas and catalytically converts it to synthetic natural gas (i.e., methane) using H₂ generated from renewable sources. The Ru in the DFM, in combination with H₂, catalytically hydrogenates both adsorbed CO₂ and the bulk Na₂CO₃, forming methane. The depleted sites adsorb CO₂ through a carbonate reformation process and in addition adsorb CO₂ on its surface. This material functions well in O₂- and H₂O-containing flue gas where the favorable Ru redox property allows RuO_x, formed during flue gas exposure, to be reduced during the hydrogenation cycle. As a combined CO₂ capture and utilization scheme, this technology overcomes many of the limitations of the conventional liquid amine-based CO₂ sorbent technology. Full article

Density functional theory (DFT) calculations have been used to describe the first turnover of an olefin metathesis reaction calling for a new in silico family of homogenous Ru-based catalysts bearing a phosphine–phosphonium ylide ligand, with ethylene as a substrate. Equal to conventional Ru-based catalysts bearing an N-heterocyclic carbene (NHC) ligand, the activation of these congeners occurs through a dissociative mechanism, with a more exothermic first phosphine dissociation step. In spite of a stronger electron-donating ability of a phosphonium ylide C-ligand with respect to a diaminocarbene analogue, upper energy barriers were calculated to be on average ca. 5 kcal/mol higher than those of Ru–NHC standards. Overall, the study also highlights advantages of bidentate ligands over classical monodentate NHC and phosphine ligands, with a particular preference for the cis attack of the olefin. The new generation of catalysts is constituted by cationic complexes potentially soluble in water, to be compared with the typical neutral Ru–NHC ones. Full article

New hybrid catalysts based on Ru nanoparticles, encapsulated into poly(propylene imine dendrimers), immobilized into silica pores, were synthesized and examined for the hydrogenation of alkyl-substituted phenols. The corresponding alkyl-substituted cyclohexanols were presented as the major reaction products, while incomplete hydrogenation products appeared to be minor. A competition between the sterical factors of dendrimer-containing carriers and the electronic factors of substrate substituents influenced the hydrogenation rate of the alkyl-substituted phenols. The carrier structure was found to have a significant influence on both the physical and chemical properties of the catalysts and their hydrogenation activity. The synthesized hybrid catalysts appeared to be stable after recycling and could be re-used several times without significant loss of activity. Full article