Catalysts, Volume 11, Issue 1 (January 2021) – 144 articles

This article presents an overview of the reports on the doping of TiO₂ with carbon, nitrogen, and sulfur, including single, co-, and tri-doping. A comparison of the properties of the photocatalysts synthesized from various precursors of TiO₂ and C, N, or S dopants is summarized. Selected methods of synthesis of the non-metal doped TiO₂ are also described. Furthermore, the influence of the preparation conditions on the doping mode (interstitial or substitutional) with reference to various types of the modified TiO₂ is summarized. The mechanisms of photocatalysis for the different modes of the non-metal doping are also discussed. Moreover, selected applications of the non-metal doped TiO₂ photocatalysts are shown, including the removal of organic compounds from water/wastewater, air purification, production of hydrogen, lithium storage, inactivation of bacteria, or carbon dioxide reduction. Full article

Molybdenum phosphide (MoP) catalyzes the hydrogenation of CO, CO₂, and their mixtures to methanol, and it is investigated as a high-activity catalyst that overcomes deactivation issues (e.g., formate poisoning) faced by conventional transition metal catalysts. MoP as a new catalyst for hydrogenating CO₂ to methanol is particularly appealing for the use of CO₂ as chemical feedstock. Herein, we use a colloidal synthesis technique that connects the presence of MoP to the formation of methanol from CO₂, regardless of the support being used. By conducting a systematic support study, we see that zirconia (ZrO₂) has the striking ability to shift the selectivity towards methanol by increasing the rate of methanol conversion by two orders of magnitude compared to other supports, at a CO₂ conversion of 1.4% and methanol selectivity of 55.4%. In situ X-ray Absorption Spectroscopy (XAS) and in situ X-ray Diffraction (XRD) indicate that under reaction conditions the catalyst is pure MoP in a partially crystalline phase. Results from Diffuse Reflectance Infrared Fourier Transform Spectroscopy coupled with Temperature Programmed Surface Reaction (DRIFTS-TPSR) point towards a highly reactive monodentate formate intermediate stabilized by the strong interaction of MoP and ZrO₂. This study definitively shows that the presence of a MoP phase leads to methanol formation from CO₂, regardless of support and that the formate intermediate on MoP governs methanol formation rate. Full article

In recent years, we have experienced extreme climate changes due to the global warming, continuously impacting and changing our daily lives. To build a sustainable environment and society, various energy technologies have been developed and introduced. Among them, energy harvesting, converting ambient environmental energy into electrical energy, has emerged as one of the promising technologies for a variety of energy applications. In particular, a photo (electro) catalytic water splitting system, coupled with emerging energy harvesting technology, has demonstrated high device performance, demonstrating its great social impact for the development of the new water splitting system. In this review article, we introduce and discuss in detail the emerging energy-harvesting technology for photo (electro) catalytic water splitting applications. The article includes fundamentals of photocatalytic and electrocatalytic water splitting and water splitting applications coupled with the emerging energy-harvesting technologies using piezoelectric, piezo-phototronic, pyroelectric, triboelectric, and photovoltaic effects. We comprehensively deal with different mechanisms in water splitting processes with respect to the energy harvesting processes and their effect on the water splitting systems. Lastly, new opportunities in energy harvesting-assisted water splitting are introduced together with future research directions that need to be investigated for further development of new types of water splitting systems. Full article

In this work, a detailed computational study on a recently synthetized Mn(I)-dependent complex [(^tBuPNNOP)Mn(CO)₂]⁺ is reported. This species promotes the dehydrogenation of formic acid to carbon dioxide and hydrogen. The here proposed catalytic cycle proceeds through the formation of stabilized adduct between [(^tBuPNNOP^tBu)Mn(CO)₂]⁺ and formate and the progressive release of CO₂ and H₂, mediated by the presence of trimethylamine. In order to evaluate the influence of the environment on the catalytic activity, different solvents have been taken into account. The computed barriers and the geometrical parameters account well for the available experimental data, confirming the robustness of the complex and reproducing its good catalytic performance. Outcomes from the present investigation can stimulate further experimental works in the design of new more efficient catalysts devoted to H₂ production. Full article

Recent studies have highlighted the therapeutic and ergogenic potential of the ketone body ester, (R)-3-hydroxybutyl-(R)-3-hydroxybutyrate. In the present work, the enzymatic synthesis of this biological active compound is reported. The (R)-3-hydroxybutyl-(R)-3-hydroxybutyrate has been produced through the transesterification of racemic ethyl 3-hydroxybutyrate with (R)-1,3-butanediol by exploiting the selectivity of Candida antarctica lipase B (CAL-B). The needed (R)-1,3-butanediol was in turn obtained from the kinetic resolution of the racemate achieved by acetylation with vinyl acetate, also in this case, thanks to the enantioselectivity of the CAL-B used as catalyst. Finally, the stereochemical inversion of the unreacted (S) enantiomers of the ethyl 3-hydroxybutyate and 1,3-butanediol accomplished by known procedure allowed to increase the overall yield of the synthetic pathway by incorporating up to 70% of the starting racemic reagents into the final product. Full article

There is significant environmental concern about chlorinated organic compounds (COCs) in wastewater, surface water, and groundwater due to their low biodegradability and high persistence. In this work, 1,2,4-trichlorobenzene (124-TCB) was selected as a model compound to study its abatement using wet peroxide oxidation at neutral pH with goethite as a heterogeneous catalyst, which was enhanced with visible monochromatic light-emitting diode (LED) light (470 nm). A systematic study of the main operating variables (oxidant and catalyst concentration and irradiance) was accomplished to investigate their influence in the abatement of 124-TCB in water. The reaction was carried out in a well-mixed reactor of glass irradiated by a visible LED light. The hydrogen peroxide concentration was tested from 0 to 18 mM, the goethite concentration within the range 0.1–1.0 g·L⁻¹ and the irradiance from 0.10 to 0.24 W·cm⁻² at neutral pH. It was found that this oxidation method is a very efficient technique to abate 124-TCB, reaching a pollutant conversion of 0.9 when using 0.1 g·L⁻¹ of goethite, 18 mM of H₂O₂, and 0.24 of W·cm⁻². Moreover, the system performance was evaluated using the photonic efficiency (ratio of the moles of 124-TCB abated and the moles of photons arriving at the reactor window). The maximum photonic efficiencies were obtained using the lowest lamp powers and moderate to high catalyst loads. Full article

Improved yields of, and selectivities to, value-added products synthesised from glycerol are shown to be achieved through the judicious selection of dehydrating agents and through the development of improved catalysts. The direct carboxylation of glycerol with CO₂ over lanthanum-based catalysts can yield glycerol carbonate in the presence of basic species, or acetins in the presence of acidic molecules. The formation of glycerol carbonate is thermodynamically limited; removal of produced water shifts the chemical equilibrium to the product side. Acetonitrile, benzonitrile and adiponitrile have been investigated as basic dehydrating agents to promote glycerol carbonate synthesis. In parallel, acetic anhydride has been studied as an acidic dehydrating agent to promote acetin formation. Alongside this, the influence of the catalyst synthesis method has been investigated allowing links between the physicochemical properties of the catalyst and catalytic performance to be determined. The use of acetonitrile and La catalysts allows the results for the novel dehydrating agents to be benchmarked against literature data. Notably, adiponitrile exhibits significantly enhanced performance over other dehydrating agents, e.g., achieving a 5-fold increase in glycerol carbonate yield with respect to acetonitrile. This is in part ascribed to the fact that each molecule of adiponitrile has two nitrile functionalities to promote the reactive removal of water. In addition, mechanistic insights show that adiponitrile results in reduced by-product formation. Considering by-product formation, 4-hydroxymethyl(oxazolidin)-2-one (4-HMO) has, for the first time, been observed in all reaction systems using cyanated species. Studies investigating the influence of the catalyst synthesis route show a complex relationship between surface basicity, surface area, crystallite phase and reactivity. These results suggest alternative strategies to maximise the yield of desirable products from glycerol through tailoring the reaction chemistry and by-product formation via an appropriate choice of dehydrating agents and co-reagents. Full article

Four vinyl polymer gels (VPGs) were synthesized by free radical polymerization of divinylbenzene, ethane-1,2-diyl dimethacrylate, and copolymerization of divinylbenzene with styrene, and ethane-1,2-diyl dimethacrylate with methyl methacrylate, as supports for palladium nanoparticles. VPGs obtained from divinylbenzene and from divinylbenzene with styrene had spherical shapes while those obtained from ethane-1,2-diyl dimethacrylate and from ethane-1,2-diyl dimethacrylate with methyl methacrylate did not have any specific shapes. Pd(OAc)₂ was impregnated onto VPGs and reduced to form Pd⁰ nanoparticles within VPGs. The structures of Pd⁰-loaded VPGs were analyzed by XRD, TEM, and nitrogen gas adsorption. Pd⁰-loaded VPGs had nanocrystals of Pd⁰ within and on the surface of the polymeric supports. Pd⁰/VPGs efficiently catalyzed the oxidation/disproportionation of benzyl alcohol into benzaldehyde/toluene, where activity and selectivity between benzaldehyde and toluene varied, depending on the structure of VPG and the weight percentage loading of Pd⁰. The catalysts were stable and Pd leaching to liquid phase did not occur. The catalysts were separated and reused for five times without any significant decrease in the catalytic activity. Full article

In the synthesis method of a BiVO₄ photoanode via BiOI flakes, a BiOI film is formed by electrochemical deposition in Step 1, and a vanadium (V) source solution is placed by drop-casting on the BiOI film in Step 2. Following this, BiVO₄ particles are converted from the BiOI–(V species) precursors by annealing. However, it is challenging to evenly distribute vanadium species among the BiOI flakes. As a result, the conversion reaction to form BiVO₄ does not proceed simultaneously and uniformly. To address this limitation, in Step 2, we developed a new electrochemical deposition method that allowed the even distribution of V₂O₅ among Bi–O–I flakes to enhance the conversion reaction uniformly. Furthermore, when lactic acid was added to the electrodeposition bath solution, BiVO₄ crystals with an increased (040) peak intensity of the X-ray diffractometer (XRD) pattern were obtained. The photocurrent of the BiVO₄ photoanode was 2.2 mA/cm² at 1.23 V vs. reversible hydrogen electrode (RHE) under solar simulated light of 100 mW/cm² illumination. The Faradaic efficiency of oxygen evolution was close to 100%. In addition, overall water splitting was performed using a Ru/SrTiO₃:Rh–BiVO₄ photocatalyst sheet prepared by the BiVO₄ synthesis method. The corresponding hydrogen and oxygen were produced in a 2:1 stoichiometric ratio under visible light irradiation. Full article

Novel flower-shaped C-dots/Co₃O₄{111} with dual-reaction centers were constructed to improve the Fenton-like reaction activity and peroxymonosulfate (PMS) conversion to sulfate radicals. Due to the exposure of a high surface area and Co₃O₄{111} facets, flower-shaped C-dots/Co₃O₄{111} could provide more Co(II) for PMS activation than traditional spherical Co₃O₄{110}. Meanwhile, PMS was preferred for adsorption on Co₃O₄{111} facets because of a high adsorption energy and thereby facilitated the electron transfer from Co(II) to PMS. More importantly, the Co–O–C linkage between C-dots and Co₃O₄{111} induced the formation of the dual-reaction center, which promoted the production of reactive organic radicals (R•). PMS could be directly reduced to SO₄⁻• by R• over C-dots. On the other hand, electron transferred from R• to Co via Co–O–C linkage could accelerate the redox of Co(II)/(III), avoiding the invalid decomposition of PMS. Thus, C-dots doped on Co₃O₄{111} improved the PMS conversion rate to SO₄⁻• over the single active site, resulting in high turnover numbers (TONs). In addition, TPR analysis indicated that the optimal content of C-dots doped on Co₃O₄{111} is 2.5%. More than 99% of antibiotics and dyes were degraded over C-dots/Co₃O₄{111} within 10 min. Even after six cycles, C-dots/Co₃O₄{111} still remained a high catalytic activity. Full article

A biocatalytic cascade system using a cocktail of oxidoreductase enzymes (2-1B peroxidase and M120 laccase) was designed for the allylic oxidation of (+)-α-pinene into value-added products (e.g., verbenol and verbenone). The oxidative transformation involved a two-step process as follows: (+)-α-pinene was (i) oxidized on the allylic position with H₂O₂ mainly assisted by 2-1B peroxidase leading to verbenol as the principal reaction product, and (ii) directed to verbenone in the presence of M120 laccase responsible for further oxidation of verbenol to verbenone. The reaction environment was ensured by the acetate buffer (0.1 M, pH = 5). Optimum values for the experimental parameters (e.g., concentration of 2-1B peroxidase, M120 laccase, and H₂O₂) were set up. The biocatalytic cascade process was monitored for 24 h in order to evaluate the process pathway. Maximum performance under optimum conditions was reached after 5 h incubation time (e.g., 80% (+)-α-pinene conversion and 70% yield in verbenol). Therefore, the developed biocatalytic cascade system offered promising perspectives for (+)-α-pinene valorization. Full article

This work focuses on the support effect of the performances of Co based catalysts for acetic acid steam reforming. SBA-15, a well ordered hexagonal mesoporous silica structure, and CeO₂ have been selected as the supports, with the impact of chromium addition also being investigated. Better acetic acid steam reforming performances have been recorded for CeO₂ compared to SBA-15 supported catalysts and, in particular, the 7Co/CeO₂ catalyst showed the highest values of acetic acid conversions with enhanced H₂ yields below 480 °C, in comparison to the other investigated catalytic formulations. In addition, more pronounced coke depositions and acetone concentrations have been obtained with CeO₂ supported catalysts, due to the tendency of ceria to catalyse the ketonization reaction. Chromium addition to Co/SBA-15 catalysts led to an enhancement in the activity towards acetic acid steam reforming, while on CeO₂ supported catalysts no improvement in the catalysts’ activity was observed. However, on both SBA-15 and CeO₂ supported catalysts, Cr addition reduced the amount of coke deposited on the catalysts surface. Full article

Rare ginsenoside Rh2 exhibits diverse pharmacological effects. UDP-glycosyltransferase (UGT) catalyzed glycosylation of protopanaxadiol (PPD) has been of growing interest in recent years. UDP-glycosyltransferase Bs-YjiC coupling sucrose synthase in one-pot reaction was successfully applied to ginsenoside biosynthesis with UDP-glucose regeneration from sucrose and UDP, which formed a green and sustainable approach. In this study, the his-tagged UDP-glycosyltransferase Bs-YjiC mutant M315F and sucrose synthase AtSuSy were co-immobilized on heterofunctional supports. The affinity adsorption significantly improved the capacity of specific binding of the two recombinant enzymes, and the dual enzyme covalently cross-linked by the acetaldehyde groups significantly promoted the binding stability of the immobilized bienzyme, allowing higher substrate concentration by easing substrate inhibition for the coupled reaction. The dual enzyme amount used for ginsenoside Rh2 biosynthesis is Bs-YjiC-M315F: AtSuSy = 18 mU/mL: 25.2 mU/mL, a yield of 79.2% was achieved. The coimmobilized M315F/AtSuSy had good operational stability of repetitive usage for 10 cycles, and the yield of ginsenoside Rh2 was kept between 77.6% and 81.3%. The high titer of the ginsenoside Rh2 cumulatively reached up to 16.6 mM (10.3 g/L) using fed-batch technology, and the final yield was 83.2%. This study has established a green and sustainable approach for the production of ginsenoside Rh2 in a high level of titer, which provides promising candidates for natural drug research and development. Full article

Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO₂ aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO₂ catalysts were investigated using carbon monoxide (CO) oxidation as a model reaction. The catalyst becomes active, and the conversion increases after the temperature reaches the ignition temperature (T_ig). A normal hysteresis in carbon monoxide (CO) oxidation has been observed, where the catalysts continue to exhibit high catalytic activity (CO conversion remains at 100%) during the extinction even at temperatures lower than T_ig. The catalyst was characterized using BET, TEM, XPS, TGA-DSC, and FTIR. In this work, the influence of pretreatment conditions and stability of the active sites on the catalytic activity and hysteresis is presented. The CO oxidation on the Pd/SiO₂ catalyst has been attributed to the dissociative adsorption of molecular oxygen and the activation of the C-O bond, followed by diffusion of adsorbates at T_ig to form CO₂. Whereas, the hysteresis has been explained by the enhanced stability of the active site caused by thermal effects, pretreatment conditions, Pd-SiO₂ support interaction, and PdO formation and decomposition. Full article

Multi-metallic Pd@FePt core–shell nanoparticles were synthesized using a direct seed-mediated growth method, consisting of facile and mild procedures, to increase yield. The Fe/Pt ratio in the shell was easily controlled by adjusting the amount of Fe and Pt precursors. Furthermore, compared with commercial Pt/C catalysts, Pd@FePt nanoparticles exhibited excellent activity and stability toward the methanol oxidation reaction (MOR), making them efficient in direct methanol fuel cells (DMFC). Full article

Susceptibility of soybean phosphatidylcholine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and its phosphono analogue (R)-2,3-dipalmitoyloxypropylphosphonocholine (DPPnC) towards selected lipases and phospholipases was compared. The ethanolysis of substrates at sn-1 position was carried out by lipase from Mucor miehei (Lipozyme^®) and lipase B from Candida antarctica (Novozym 435) in 95% ethanol at 30 °C, and the hydrolysis with Lecitase^TM Ultra was carried out in hexane/water at 50 °C. Hydrolysis at sn-2 position was carried out in isooctane/Tris-HCl/AOT system at 40 °C using phospholipase A₂ (PLA₂) from porcine pancreas and PLA₂ from bovine pancreas or 25 °C using PLA₂ from bee venom. Hydrolysis in the polar part of the studied compounds was carried out at 30 °C in acetate buffer/ethyl acetate system using phospholipase D (PLD) from Streptococcus sp. and PLD from white cabbage or in Tris-HCl buffer/methylene chloride system at 35 °C using PLD from Streptomyces chromofuscus. The results showed that the presence of C-P bond between glycerol and phosphoric acid residue in DPPnC increases the rate of enzymatic hydrolysis or ethanolysis of ester bonds at the sn-1 and sn-2 position and decreases the rate of hydrolysis in the polar head of the molecule. The most significant changes in the reaction rates were observed for reaction with PLD from Streptococcus sp. and PLD from Streptomyces chromofuscus that hydrolyzed DPPnC approximately two times slower than DPPC and soybean PC. The lower susceptibility of DPPnC towards enzymatic hydrolysis by phospholipases D gives hope for the possibility of using DPPnC-like phosphonolipids as the carriers of bioactive molecules that, instead of choline, can be bounded with diacylpropylphosphonic acids (DPPnA). Full article

Catalytic propane dehydrogenation is an attractive method to produce propylene while avoiding the issues of its traditional synthesis via naphtha steam cracking of naphtha. In this contribution, a series of Pt-Sn/SBA-16 catalysts were synthesized and evaluated for this purpose. Bimetallic Pt-Sn catalysts were more active than catalysts containing only Pt. The catalyst with the best performance was assessed at different reaction times of 0, 60, 180, and 300 min. The evolution of coke deposits was also studied. Thermogravimetric analysis demonstrated the presence of two types of coke on the catalyst surface at low and high temperature, respectively. Raman results showed an increased coke’s crystal size from 60 to 180 min on stream, and from 180 to 300 min under reaction, Raman suggested a reduction in the crystal size of coke. Also transmission electron microscopy confirmed a more evident agglomeration of metallic particles with reaction times higher than 180 min. These results are consistent with the phenomena called “coke migration” and the cause is often explained by coke movement near the particle to the support; it can also be explained due to sintering of the metallic particle, which we propose as a more suitable explanation. Full article

As a promising material for heterogeneous catalytic applications, layered iron (II) monosulfide (FeS) contains active edges and an inert basal (001) plane. Activating the basal (001) plane could improve the catalytic performance of the FeS material towards CO₂ activation and reduction reactions. Herein, we report dispersion-corrected density functional theory (DFT-D3) calculations of the adsorption of CO₂ and the elementary steps involved in its reduction through the reverse water-gas shift reaction on a defective FeS (001) surface containing sulfur vacancies. The exposed Fe sites resulting from the creation of sulfur vacancies are shown to act as highly active sites for CO₂ activation and reduction. Based on the calculated adsorption energies, we show that the CO₂ molecules will outcompete H₂O and H₂ molecules for the exposed active Fe sites if all three molecules are present on or near the surface. The CO₂ molecule is found to weakly physisorb (−0.20 eV) compared to the sulfur-deficient (001) surface where it adsorbs much strongly, releasing adsorption energy of −1.78 and −1.83 eV at the defective FeS (001) surface containing a single and double sulfur vacancy, respectively. The CO₂ molecule gained significant charge from the interacting surface Fe ions at the defective surface upon adsorption, which resulted in activation of the C–O bonds confirmed via vibrational frequency analyses. The reaction and activation energy barriers of the elementary steps involved in the CO₂ hydrogenation reactions to form CO and H₂O species are also unraveled. Full article

In this work, the PIL (poly ionic liquid)@TiO₂ composite was designed with two polymerized ionic liquid concentrations (low and high) and evaluated for pollutant degradation activity for benzene and toluene. The results showed that PIL (low)@TiO₂ composite was more active than PIL (high)@TiO₂ composites. The photodegradation rate of benzene and toluene pollutants by PIL (low)@TiO₂ and PIL (high)@TiO₂ composites was obtained as 86% and 74%, and 59% and 46%, respectively, under optimized conditions. The bandgap of TiO₂ was markedly lowered (3.2 eV to 2.2 eV) due to the formation of PIL (low)@TiO₂ composite. Besides, graphene oxide (GO) was used to grow the nano-photocatalysts’ specific surface area. The as-synthesized PIL (low)@TiO₂@GO composite showed higher efficiency for benzene and toluene degradation which corresponds to 91% and 83%, respectively. The resultant novel hybrid photocatalyst (PIL@TiO₂/m-GO) was prepared and appropriately characterized for their microstructural, morphology, and catalytic properties. Among the studied photocatalysts, the PIL (low)@TiO₂@m-GO composite exhibits the highest activity in the degradation of benzene (97%) and toluene (97%). The ultimate bandgap of the composite reached 2.1 eV. Our results showed that the as-prepared composites hold an essential role for future considerations over organic pollutants. Full article

Today, the theme of environmental preservation plays an important role within the activities of the scientific community and influences the choices of politics and the common population. In this context, the use of non-fossil substances should be promoted for different reasons: to avoid the depletion and damage of the areas involved in the fossil fuel extraction, decrease the impact of emissions/by-products related to the industrial transformation of fossil-based products and possibly exploit residual biomasses as sources of carbon. This latter aspect also can be viewed as a way to revalorize lignocellulose waste, generally destined to dump as putrescible matter or to be incinerated. In this review, we are aiming to present a concise overview of the multiple functions of lignocellulose biomass in the broad field of catalysis for a sustainable development. The originality of the approach is considering the lignocellulose-derived matter in three different aspects: (i) as a precursor to convert into platform molecules, (ii) as an active material (i.e., humic-like substances as photosensitizers) and (iii) as a green support for catalytic applications. We find that this perspective can widen the awareness level of scientists involved in the catalysis field for the exploitation of residual biomass as a valuable and complementary resource. Full article

In this study, the contamination of H⁺ZSM-5 catalyst by calcium, potassium and sodium was investigated by deactivating the catalyst with various concentrations of these inorganics, and the subsequent changes in the properties of the catalyst are reported. Specific surface area analysis of the catalysts revealed a progressive reduction with increasing concentrations of the inorganics, which could be attributed to pore blocking and diffusion resistance. Chemisorption studies (NH₃-TPD) showed that the Bronsted acid sites on the catalyst had reacted with potassium and sodium, resulting in a clear loss of active sites, whereas the presence of calcium did not appear to cause extensive chemical deactivation. Pyrolysis experiments revealed the progressive loss in catalytic activity, evident due the shift in selectivity from producing only aromatic hydrocarbons (benzene, toluene, xylene, naphthalenes and others) with the fresh catalyst to oxygenated compounds such as phenols, guaiacols, furans and ketones with increasing contamination by the inorganics. The carbon yield of aromatic hydrocarbons decreased from 22.3% with the fresh catalyst to 1.4% and 2.1% when deactivated by potassium and sodium at 2 wt %, respectively. However, calcium appears to only cause physical deactivation. Full article

Recently, there have been numerous efforts to develop hydrogen-rich organic materials because hydrogen energy is emerging as a renewable energy source. In this regard, we designed and prepared four new materials based on N-alkyl-bis(carbazole), 9,9′-(2-methylpropane-1,3-diyl)bis(9H-carbazole) (MBC), 9,9′-(2-ethylpropane-1,3-diyl)bis(9H-carbazole) (EBC), 9,9′-(2-propylpropane-1,3-diyl)bis(9H-carbazole) (PBC), and 9,9′-(2-butylpropane-1,3-diyl)bis(9H-carbazole) (BBC), to investigate their hydrogen adsorption/hydrogen desorption reactivity depending on the length of the alkyl chain. The gravimetric densities of MBC, EBC, PBC, and BBC were 5.86, 5.76, 5.49, and 5.31 H₂ wt %, respectively, again depending on the alkyl chain length. All materials showed complete hydrogenation reactions under ruthenium on an alumina catalyst at 190 °C, and complete reverse reactions and dehydrogenation reactions were observed under palladium on an alumina catalyst at <280 °C. At this temperature, all the prepared compounds were thermally stable, and no decomposition was observed. Full article

The first remarkable property associated to metallophthalocyanines (MPcs) was their chemical “inertness”, which made and make them very attractive as stable and durable industrial dyes. Nevertheless, their rich redox chemistry was also explored in the last decades, making available a solid and detailed knowledge background for further studies on the suitability of MPcs as redox catalysts. An overlook of MPcs and their catalytic activity with dioxygen as oxidants will be discussed here with a special emphasis on the last decade. The mini-review begins with a short introduction to phthalocyanines, from their structure to their main features, going then through the redox chemistry of metallophthalocyanines and their catalytic activity in aerobic oxidation reactions. The most significant systems described in the literature comprise the oxidation of organosulfur compounds such as thiols and thiophenes, the functionalization of alkyl arenes, alcohols, olefins, among other substrates. Full article

Ni-based catalysts are prone to agglomeration and carbon deposition at high temperatures. Therefore, the development of Ni-based catalysts with high activities at low temperatures is a very urgent and challenging research topic. Herein, Ni-based nanocatalysts containing Co promoter with mosaic structure were prepared by reduction of NiCoAl-LDHs, and used for CO₂ methanation. When the reaction temperature is 250 °C (0.1 MPa, GHSV = 30,000 mL·g⁻¹·h⁻¹), the conversion of CO₂ on the NiCo_0.5Al-R catalyst reaches 81%. However, under the same test conditions, the conversion of CO₂ on the NiAl-R catalyst is only 26%. The low-temperature activity is significantly improved due to Co which can effectively control the size of the Ni particles, so that the catalyst contains more active sites. The CO₂-TPD results show that the Co can also regulate the number of moderately basic sites in the catalyst, which is beneficial to increase the amount of CO₂ adsorbed. More importantly, the NiCo_0.5Al-R catalyst still maintains high catalytic performance after 92 h of continuous reaction. This is due to the confinement effect of the AlO_x substrate inhibiting the agglomeration of Ni nanoparticles. The Ni-based catalysts with high performance at low temperature and high stability prepared by the method used have broad industrial application prospects. Full article

A facile, sustainable method for the selective modification of aliphatic hydroxy (R–OH) groups in Kraft lignin was developed using an ionic liquid, 1-ethyl-3-methylimidazolium acetate (EmimOAc), as a solvent and catalyst. Selective R–OH modification was achieved by a one-pot, two-step homogeneous reaction: (i) acetylation of R–OH and aromatic OH (Ar–OH) groups with isopropenyl acetate (IPAc) as an acyl donor and (ii) subsequent selective deacetylation of the generated aromatic acetyl (Ar–OAc) groups. In step (i), IPAc reacts rapidly with Ar–OH but slowly with R–OH. The generated Ar–OAc is gradually deacetylated by heating in EmimOAc, whereas the aliphatic acetyl (R–OAc) groups are chemically stable. In step (ii), all R–OH is acetylated by IPAc and Ar–OAc which is a better acyl donor than IPAc, contributing to the rapid acetylation of the remaining R–OH, and selective deacetylation of the residual Ar–OAc is completed by adding a tiny amount of water as a proton source. This two-step reaction resulted in selective R–OH modification (>99%) in Kraft lignin with the remaining being almost all Ar–OH groups (93%). Selectively modified Kraft lignin was obtained with an acceptably high isolated yield (85%) and repeatability (N = 3). Furthermore, despite the lower substitution degree, it exhibited solubility in common solvents, heat-meltability, and thermal stability comparable to completely acetylated Kraft lignin. Full article

Two different preparation methods, viz. incipient impregnation and mechanical mixing, have been used to prepare V-based oxygen carriers with different V loadings for chemical looping oxidative dehydrogenation of propane. The effect of the preparation method, V loading, and reaction temperature on the performance of these oxygen carriers have been measured and discussed. It was found that the VO_x species can be well distributed on the support when the V loading is low (5 wt.% and 10 wt.%), but they may become aggregated at higher loadings. For oxygen carriers with a higher V loading, the oxygen transport capacity of the oxygen carrier, propane conversion and CO_x selectivities increase, while the propylene selectivity decreases. With a V-loading of 10 wt.%, the maximum propylene yield was achieved. The VO_x species were better distributed over the support when applying the impregnation method; however, at higher V loadings the V-based oxygen carriers prepared by mechanical mixing showed a larger oxygen transport capacity. The oxygen carriers prepared by impregnation showed a better performance for the oxidative dehydrogenation of propane (ODHP) and re-oxidation reactions compared to oxygen carriers prepared by mechanical mixing. Higher reaction temperatures are favorable for the re-oxidation reaction, but unfavorable for the propylene production. Full article

The current climate crisis warrants investigation into alternative fuel sources. The hydrolysis reaction of an aqueous hydride precursor, and the subsequent production of hydrogen gas, prove to be a viable option. A network of beta-cyclodextrin capped gold nanoparticles (BCD-AuNP) was synthesized and subsequently characterized by Powder X-Ray Diffraction (P-XRD), Fourier Transform Infrared (FTIR), Transmission Electron Microscopy (TEM), and Ultraviolet-Visible Spectroscopy (UV-VIS) to confirm the presence of gold nanoparticles as well as their size of approximately 8 nm. The catalytic activity of the nanoparticles was tested in the hydrolysis reaction of sodium borohydride. The gold catalyst performed best at 303 K producing 1.377 mL min⁻¹ mL_cat⁻¹ of hydrogen. The activation energy of the catalyst was calculated to be 54.7 kJ/mol. The catalyst resisted degradation in reusability trials, continuing to produce hydrogen gas in up to five trials. Full article

Degradation of organic dyes and their byproducts by heterogeneous photocatalysts is an essential process, as these dyes can be potentially discharged in wastewater and threaten aquatic and xerophyte life. Therefore, their complete mineralization into nontoxic components (water and salt) is necessary through the process of heterogeneous photocatalysis. In this study, Zr/CrO₂ (Zirconium-doped chromium IV oxide) nanocomposite-based photocatalysts with different compositions (1, 3, 5, 7 & 9 wt.%) were prepared by an environmentally friendly, solid-state reaction at room temperature. The as-prepared samples were calcined under air at 450 °C in a furnace for a specific period of time. The synthesis of Zr/CrO₂ photocatalysts was confirmed by various techniques, including XRD, SEM, EDX, FT-IR, UV-Vis, and BET. The photocatalytic properties of all samples were tested towards the degradation of methylene blue and methyl orange organic dyes under UV light. The results revealed a concentration-dependent photocatalytic activity of photocatalysts, which increased the amount of dopant (up to 5 wt.%). However, the degradation efficiency of the catalysts decreased upon further increasing the amount of dopant due to the recombination of holes and photoexcited electrons. Full article

Infrared spectroscopy is typically not used to establish the oxidation state of metal-based catalysts. In this work, we show that the baseline of spectra collected in diffuse reflectance mode of a series of Pd/Al₂O₃ samples of increasing Pd content varies significantly and reversibly under alternate pulses of CO or H₂ and O₂. Moreover, these baseline changes are proportional to the Pd content in Pd/Al₂O₃ samples exhibiting comparable Pd particle size. Similar measurements by X-ray absorption spectroscopy on a different 2 wt.% Pd/Al₂O₃ confirm that the baseline changes reflect the reversible reduction-oxidation of Pd. Hence, we demonstrate that changes in oxidation state of metal-based catalysts can be determined using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and that this behavior is part of the spectral changes that are returned by experiments under operando conditions. Full article

Oxidation of 5-hydroxymethylfurfural (HMF), a major feedstock derived from waste/fresh biomass, into 2,5-furandicarboxylic acid (FDCA) is an important transformation for the production of biodegradable plastics. Herein, we investigated the effect of the support (unmodified and modified titania, commercial alumina, and untreated and treated Sibunit carbon) of mono- and bimetallic catalysts based on noble metals (Ag, Au, Pd) on selective HMF oxidation with molecular oxygen to FDCA under mild and basic reaction conditions. The higher selectivity to FDCA was obtained when metals were supported on Sibunit carbon (Cp). The order of noble metal in terms of catalyst selectivity was: Ag < Au < Pd < PdAu. Finally, FDCA production on the most efficient PdAu NPs catalysts supported on Sibunit depended on the treatment applied to this carbon support in the order: PdAu/Cp < PdAu/Cp-HNO₃ < PdAu/Cp-NH₄OH. These bimetallic catalysts were characterized by nitrogen adsorption-desorption, inductively coupled plasma atomic emission spectroscopy, high resolution transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Hammet indicator method and X-ray photoelectron spectroscopy. The functionalization of Sibunit surface by HNO₃ and NH₄OH led to a change in the contribution of the active states of Pd and Au due to promotion effect of N-doping and, as a consequence, to higher FDCA production. HMF oxidation catalyzed by bimetallic catalysts is a structure sensitive reaction. Full article