Catalysts

Palladium–bismuth nanomaterials are used in various chemical applications such detectors, electrodes, and catalysts. Pd-Bi catalysts are attracting widespread interest because these catalysts enable the production of valuable products quickly and efficiently, and are environmentally friendly. However, the composition of the catalyst can have a significant impact on its catalytic performance. In this work, we identified a correlation between the composition of the catalyst and its efficiency in converting glucose into sodium gluconate. It was found that the conversion decreases with increasing bismuth content. The most active catalyst was the 0.35Bi:Pd sample with a lower bismuth content (glucose conversion of 57%). TEM, SEM, EXAFS, and XANES methods were used to describe, in detail, the surface properties of the xBi:Pd/Al₂O₃ catalyst samples. The increase in particle size with increasing bismuth content, observed in the TEM micrographs, was associated with the low melting point of bismuth (271 °C). The SEM method showed that palladium and bismuth particles were uniformly distributed over the surface of the support in close proximity to each other, which allowed us to conclude that an alloy of non-stoichiometric composition was formed. The EXAFS and XANES methods established that bismuth was located on the surface of the nanoparticle predominantly in an oxidized state. Full article

Resource utilization of sludge is critical because traditional sludge treatment methods cause a large amount of nutrient loss. This study investigated the impact of hydrochloric acid quantity, reaction temperature, and time on phosphorus release and migration from municipal sludge during hydrothermal treatment and designed a sludge disposal method for the recovery and utilization of phosphorus resources. We know that hydrochloric acid destroys the complexation of calcium and phosphorus precipitates, leading to the selective transfer of phosphorus to the liquid phase, and that the addition of 1–5% hydrochloric acid corresponds to a phosphorus extraction rate in the range of 0.3–98%. When hydrochloric acid is added, a change in temperature and reaction time has a negligible effect on phosphorus. Phosphorus can be recovered using the liquid product obtained under the optimal hydrothermal reaction conditions (adding 5% HCl at 205 °C for 30 min). After adjusting the pH value and adding the magnesium source, struvite (MgNH₄PO₄·6H₂O) can be precipitated quickly and with high purity. At a cost of USD 27.8/ton of sludge, this method can recover 94% of the phosphorus in the sludge, and the bioavailable phosphorus ratio of the product is 93%, therefore, providing an important alternative to existing phosphorus recovery technologies. Full article

Aniline, a vital component in various chemical industries, is known to be a hazardous persistent organic pollutant that can cause environmental pollution through its manufacturing, processing, and transportation. In this study, the microcosms were established using sediment with a history of aniline pollution as an inoculum to analyze the aniline biodegradation under aerobic conditions through stable isotope probing (SIP) and isopycnic density gradient centrifugation technology. During the degradation assay, aniline that was ¹³C-labeled in all six carbons was utilized to determine the phylogenetic identity of the aniline-degrading bacterial taxa that incorporate ¹³C into their DNA. The results revealed that aniline was completely degraded in the microcosm after 45 and 69 h respectively. The bacteria affiliated with Acinetobacter (up to 34.6 ± 6.0%), Zoogloea (up to 15.8 ± 2.2%), Comamonas (up to 2.6 ± 0.1%), and Hydrogenophaga (up to 5.1 ± 0.6%) genera, which are known to degrade aniline, were enriched in the heavy fractions (the DNA buoyant density was 1.74 mg L⁻¹) of the ¹³C-aniline treatments. Moreover, some rarely reported aniline-degrading bacteria, such as Prosthecobacter (up to 16.0 ± 1.6%) and Curvibacter (up to 3.0 ± 1.6%), were found in the DNA-SIP experiment. Gene families affiliated with atd, tdn, and dan were speculated to be key genes for aniline degradation based on the abundance in functional genes and diversity in different treatments as estimated using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States version 2 (PICRUSt2) and the Kyoto Encyclopedia of Genes and Genomes (KEGG). This study revealed the functional bacteria and possible degradation genes for aniline degradation in simulated polluted environments through SIP. These findings suggest that important degrading bacteria for the transformation of aniline and potential degradation pathways may be useful in the effective application of bioremediation technologies to remediate aniline-contaminated sites. Full article

Catalytic oxidation is used to control carbon monoxide (CO) emissions from industrial exhaust. In this study, a mesoporous silica material, KCC-1, was synthesized and used as a carrier with a high specific surface area to confine active component FeO_x nanoparticles (NPs), and the CO catalytic oxidation performance of x%Fe@KCC-1 catalysts (x represents the mass loading of Fe) was studied. The experimental results showed that due to its large specific surface area and abundant mesopores, the FeO_x NPs were highly dispersed on the surface of the KCC-1 carrier. The particle size of FeO_x was very small, resulting in strong interactions between FeO_x NPs and KCC-1, which enhanced the catalytic oxidation reaction on the catalyst. The FeO_x loading improved the CO adsorption capability of the catalyst, which facilitated the catalytic oxidation of CO, with the 7%Fe@KCC-1 catalyst achieving 100% CO conversion at 160°C. The CO catalytic removal mechanism was investigated by a combination of in-situ DRIFTS and DFT calculations. This study advances scientific understanding of the application potential of nano-catalysts in important oxidation reactions and provides valuable insights into the development of efficient CO oxidation catalysts. Full article

This innovative article provides a detailed description of the successful biosynthesis of zinc nanoparticles (ZnO-NPs) using an aqueous extract of Algerian Date Syrup, also known as molasses. A meticulous process was carried out to determine the optimal calcination temperature for ZnO-NPs, a crucial step in the preparation of these nanoparticles. The study was further extended by creating ZnO/rGOx nanocomposites through a hydrothermal method, varying the concentrations of reduced graphene oxide (rGO) at 5%, 10%, and 15%. The characteristics of the nanocomposites were thoroughly explored, encompassing chemical, optical, and morphological aspects, using sophisticated analysis techniques such as scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV DRS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). These analyses provided an in-depth understanding of the structure and properties of the nanocomposites. The centerpiece of this study is the evaluation of the photocatalytic degradation capacity of ZnO-NPs and ZnO/rGOx nanocomposites. These materials have demonstrated their ability to act as cost-effective and environmentally friendly photocatalysts for wastewater treatment. Experiments on methylene blue degradation under UV irradiation were conducted, yielding impressive results: a degradation efficiency of 86.6% was achieved in 140 min using 1 g/L of ZnO-NPs, and this rate reached 100% with the ZnO/rGO catalyst in the same time frame, highlighting its superiority as a photocatalyst. Furthermore, this study examined the variables affecting the photocatalysis experiment, including the solution’s pH and the amount of catalyst. The results revealed that the ZnO/rGO photocatalyst reached its optimal efficiency under neutral pH conditions and at a concentration of 1 g/L, providing crucial information for practical use of these materials. This enriched article highlights the promising potential of ZnO-NPs and ZnO/rGOx nanocomposites as efficient photocatalysts for methylene blue degradation, paving the way for significant environmental applications in wastewater treatment. Full article

This paper deals with the proposition of a kinetic model for the direct synthesis of DME via CO₂ hydrogenation in view of the necessary optimization of the catalytic system, reactor design, and process strategy. Despite the fact that DME synthesis is typically treated as a mere combination of two separated catalytic steps (i.e., methanol synthesis and methanol dehydration), the model analysis is now proposed by taking into account the improvements related to the process running over a hybrid catalyst in a rational integration of the two catalytic steps, with boundary conditions properly assumed from the thermodynamics of direct DME synthesis. Specifically, the CO₂ activation step at the metal–oxide interface in the presence of ZrO₂ has been described for the first time through the introduction of an ad hoc mechanism based on solid assumptions from inherent studies in the literature. The kinetic modeling was investigated in a tubular fixed-bed reactor operating from 200 to 260 °C between 1 and 50 bar as a function of a gas hourly space velocity ranging from 2500 to 60,000 NL/kg_cat/h, in a stoichiometric CO₂/H₂ feed mixture of 1:3 v/v. A well-detailed elementary mechanism was used to predict the CO₂ conversion rate and identify the key reaction pathways, starting with the analysis of the implicated reactions and corresponding kinetic mechanisms and expressions, and finally estimating the main parameters based on an appropriate modeling of test conditions. Full article

Direct methanol fuel cells have emerged as highly promising energy conversion devices in the past few decades. However, some challenges, such as carbon monoxide (CO) poisoning and unsatisfactory long-term stability, remain for platinum (Pt) as a methanol oxidation reaction (MOR) catalyst. This review covers recent advances in Pt alloy MOR catalysts and provides some insights. This review presents MOR catalytic mechanisms based on CO or non-CO pathways. Typical dimension-based designs of MOR catalysts, such as anisotropic nanowires, metallene, nanoframes, and corresponding rationales for performance enhancements, are introduced. More importantly, some key tuning strategies are elaborated, including intermetallic compound synthesis, interface engineering, and surface facet engineering. High-entropy alloys as an intriguing class of MOR catalysts with favorable prospects are also discussed. Finally, future directions and opportunities are outlined. Full article

This study introduces an innovative approach to sustainable biodiesel production using mussel shell-derived calcium oxide (CaO) as a catalyst for converting Jatropha curcas oil into biodiesel. By repurposing waste mussel shells, the research aims to provide an eco-friendly and cost-effective solution for environmentally responsible biodiesel production, aligning with global standards. The study involves characterizing the catalyst, optimizing reaction conditions, and achieving a remarkable 99.36% Fatty Acid Methyl Ester (FAME) yield, marking a significant step toward cleaner and more economically viable energy sources. Biodiesel, recognized for its lower emissions, is produced through transesterification using mussel shell-derived CaO as a sustainable catalyst. This research contributes to cleaner and economically viable energy sources, emphasizing the importance of sustainable energy solutions and responsible catalytic processes. This research bridges the gap between waste management, catalyst development, and sustainable energy production, contributing to the ongoing global shift towards cleaner and more economically viable energy sources. Full article

The direct oxidation of methane to methanol is considered challenging due to the intrinsically low reactivity of the C–H bond of methane and the formation of a large number of unstable intermediates (methanol, formaldehyde, and formic acid) relative to the yield of methane. However, promising advances have recently been reported in this area based on the use of electrochemical systems that differ from traditional thermal catalysis. In this review, the recent advances in direct and indirect electrochemical methane conversion with homogeneous catalysts are reviewed and discussed, especially under low-temperature conditions. Finally, the limitations of the current electrochemical methane conversion technology and future research directions are discussed. Full article

An oxygen reduction reaction (ORR) is the key half reaction of proton exchange membrane fuel cells (PEMFCs), and is highly dependent on Pt-based nanocrystals as core electrocatalysts. Despite the exceptional ORR activity from adjusting the electronic structures of surface or near-surface atoms, several serious issues, including the corrosion of carbon supports, the preferential leaching of active metal elements, the instability of surface low-coordinated atoms and the sintering/agglomeration of nanocrystals, still exist, challenging the ORR durability of developed Pt-based ORR catalysts. From the point of view of the catalyst structure design, in this review, we summarized the state-of-the-art structural regulation strategies for improving the ORR durability of Pt-based catalysts. The current limitation of Pt-based binary catalysts for ORR electrocatalysis is firstly discussed, and the detailed strategies are further classified into the optimization of supports, metal-doped alloys, core/shell structures, intermetallics and high-entropy alloys, etc. The structure–performance relationship is detailedly explained, especially emphasizing the elimination of the above restrictions. Finally, the existing challenges and future research direction are further presented, aiming at practicing the PEMFC devices of the ultradurable Pt-based catalysts. Full article

Replacing alkaline for alkaline-earth metal hydroxide in the synthesis gel during the synthesis of siliceous SSZ-13 zeolite (Si/Al~10) yields SSZ-13 with novel, advantageous properties. Its NH₄-form ion-exchanges higher amount of isolated divalent M(II) ions than the conventional one: this is the consequence of an increased number of Al pairs in the structure induced by the +2 charge of Sr(II) cations in the synthesis gel that force two charge-compensating AlO₄⁻ motives to reside closer together. We characterize the +2 state of Co(II) ions in these materials with infra-red spectroscopy and X-ray absorption spectroscopy measurements and show their utility for NOx pollutant adsorption from ambient air: the ones derived from SSZ-13 with higher Al pair content contain more isolated cobalt(II) and, thus, perform better as ambient-air NOx adsorbers. Notably, Co(II)/SSZ-13 with an increased number of Al pairs is significantly more hydrothermally stable than its NaOH-derived analogue. Loading Pd(II) into Co-SSZ-13(Sr) produces an active NOx adsorber (PNA) material that can be used for NOx adsorption from simulated diesel engine exhaust. The critical issue for these applications is hydrothermal stability of Pd-zeolites. Pd/SSZ-13 synthesized in the presence of Sr(OH)₂ does not lose its PNA capacity after extremely harsh aging at 850 and 900 °C (10 h in 10% H₂O/air flow) and loses only ~55% capacity after hydrothermal aging at 930 °C. This can be extended to other divalent metals for catalytic applications, such as copper: we show that Cu/SSZ-13 catalyst can survive hydrothermal aging at 920 °C without losing its catalytic properties, metal dispersion and crystalline structure. Thus, we provide a new, simple, and scalable strategy for making remarkably (hydro)thermally stable metal-zeolite materials/catalysts with a number of useful applications. Full article

Metal–organic framework materials (MOFs) and their derivatives are considered ideal immobilization carrier materials because of their large specific surface area, high porosity and excellent structural designability. Among them, ZIF-8 has great potential for immobilization of enzymes due to mild synthesis conditions, and good biocompatibility. However, conventional ZIF-8 crystals have poor separation and recovery efficiency due to their small pore size and poor acid stability, greatly limiting their application in enzyme immobilization and further application. Although the carbonization of ZIF-8 by pyrolysis has been shown to be one of the approaches that can enhance its chemical stability, this still does not effectively solve the problem of the difficulty of recycling. Herein, we developed a strategy of pre-carbonization immersion (immersion in aqueous FeSO₄ solution before carbonization) to synthesize ordered macroporous ZIF-8-derived carbon materials with stable ferromagnetism (denoted as CZ-x-M-y, where x denotes the carbonization temperature and y denotes the concentration of the impregnated FeSO₄ solution) and used them to immobilize lipases for biodiesel production. XRD analysis showed that the magnetic properties in the materials came from Fe₃C species. We found that the magnetic carbon materials obtained by carbonization at 600 °C showed the best immobilization effect, where CZ-600-M-0.3 (using 0.3 mol·L⁻¹ FeSO₄ aqueous solution to soak ZIF-8 and carbonized at 600 °C) had the highest enzyme loading of 183.04 mg·g⁻¹, which was 49.7% higher than that of the non-magnetic CZ-600. In addition, CZ-600-M-0.5 maintained the highest enzyme activity, which was 81.9% of the initial activity, after five batches of reuse. The stable magnetic support materials reported in this study have promising potential for the industrial application of immobilized lipase. Full article

A nanocatalyst comprising ultra-small palladium nanoparticles supported on nanodiamonds (ultra-small Pd/rNDs) was fabricated via a reduction of palladium (II) salt on oxidized nanodiamond. The prepared catalyst was characterized using XRD, XPS, ICP-MS, AAS, and TEM/HRTEM techniques, including STEM-EDS chemical mapping, which revealed that the modified material is a combination of reduced nanodiamond decorated with palladium nanoparticles. The as-prepared and well-characterized ultra-small Pd supported on rNDs displayed superb catalytic activity for Suzuki–Miyaura cross-coupling reactions at low temperature without any toxic solvents, to obtain the respective products in good-to-excellent yields (75–98%). The catalyst was easily separated from the reaction solution and was reused four times without loss of catalytic activity or chemical stability. Full article

Lignocellulosic biomass can uptake CO₂ during growth, which can then be pyrolysed into three major products, biochar (BC), syngas, and bio-oil. Due to the presence of oxygenated organic compounds, the produced bio-oil is not suitable for direct use as a fuel and requires upgrading via hydrodeoxygenation (HDO) and hydrogenation. This is typically carried out over a supported metal catalyst. Regarding circular economy and sustainability, the BC from the pyrolysis step can potentially be activated and used as a novel catalyst support, as reported here. A 15 wt% Ni/BC catalyst was developed by chemically modifying BC with sulfuric acid to improve mesoporous structure and surface area. When compared to the pristine Ni/BC catalyst, sulfuric activated Ni/BC catalyst has excellent mesopores and a high surface area, which increases the dispersion of Ni nanoparticles and hence improves the adsorptive effect and thus catalytic performance. A liquid phase hydrogenation of furfural to 2-methylfuran was performed over the developed 15 wt% Ni/BC catalyst. Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic type models for adsorption of dissociative H₂ were screened based on an R² value greater than 99%, demonstrating that the experimental data satisfactorily fit to three plausible models: competitive (Model I), competitive at only one type of adsorption site (Model II), and non-competitive with two types of adsorption sites (Model III). With a correlation coefficient greater than 99% between the experimental rates and the predicted rate, Model III, which is a dual-site adsorption mechanism involving furfural adsorption and hydrogen dissociative adsorption and surface reaction, is the best fit. The Ni/BC catalyst demonstrated comparative performance and significant cost savings over previous catalysts; a value of 24.39 kJ mol⁻¹ was estimated for activation energy, −11.43 kJ mol⁻¹ for the enthalpy of adsorption for H₂, and −5.86 kJ mol⁻¹ for furfural. The developed Ni/BC catalyst demonstrated excellent stability in terms of conversion of furfural (96%) and yield of 2-methylfuran (54%) at the fourth successive experiments. Based on furfural conversion and yield of products, it appears that pores are constructed slowly during sulfuric acid activation of the biochar. Full article

Recently, granular activated carbon (GAC) has shown its effectiveness as a cathode material for in situ ROS generation. Here, we present an electrochemically modified GAC cathode using electrode polarity reversal (PR) approach for enhanced H₂O₂ decomposition via 2-electron oxygen reduction reaction (2e-ORR). The successful GAC modification using PR necessitates tuning of the operational parameters such as frequency, current, and time intervals between the PR cycles. This modification enhances the GAC hydrophilicity by increasing the density of surface oxygen functionalities. After optimization of the electrode polarity, using the 20 (No PR)-2 (PR) interval and 140 mA current intensity, the •OH concentration reaches 38.9 $\mathsf{\mu }\mathrm{M}$ compared to the control (No PR) (28.14 $\mathsf{\mu }\mathrm{M}$). Subsequently, we evaluated the enhanced •OH generation for the removal of glyphosate, a persistent pesticide used as a model contaminant. The modified GAC using PR removed 67.6% of glyphosate compared to 40.6% by the unmodified GAC without PR, respectively. The findings from this study will advance the utilization of GAC for in situ ROS synthesis, which will have direct implications on increasing the effectiveness of electrochemical water treatment systems. Full article

Dehydration of i-PrOH is used in academic research as a test reaction to probe the acid properties of solid acid catalysts. Also, it has practical importance for the utilization of surplus acetone produced by the Hock process for the combined manufacturing of phenol and acetone as well as for the production of propene from renewable resources and waste. This study demonstrates the excellent performance of polyoxometalate acid catalysts comprising silica-supported Keggin-type heteropoly acids H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ for gas-phase i-PrOH-to-propene dehydration at ambient pressure. These catalysts show similar efficacies, giving an i-PrOH conversion and propene selectivity of 96.8 and 99.7% for 25%HPW/SiO₂ and 97.1 and 99.4% for 25%HSiW/SiO₂ in a fixed-bed reactor at 120 °C, a relevant-to-practice i-PrOH partial pressure of 15 kPa and a contact time W/F = 27 g h mol⁻¹ (GHSV = 900 mL g⁻¹ h⁻¹). The catalysts are stable, resisting deactivation for at least 24 h time on stream. The HPA/SiO₂ catalysts are superior to aluminosilicate zeolites such as H-mordenite, HZSM-5 and HY for i-PrOH-to-propene dehydration in terms of i-PrOH conversion, propene selectivity and catalyst stability. Full article

An innovative strategy has been developed to activate the basal planes in molybdenum disulfide (MoS₂) to improve their electrocatalytic activity by controlling surface electron accumulation (SEA) through aging, annealing, and nitrogen-plasma treatments. The optimal hydrogen evolution reaction (HER) performance was obtained on the surface treated with nitrogen-plasma for 120 s. An overpotential of 0.20 V and a Tafel slope of 120 mV dec⁻¹ were achieved for the optimized condition. The angle-resolved photoemission spectroscopy measurement confirmed the HER efficiency enhanced by the SEA conjugated with the sulfur vacancy active sites in the MoS₂ basal planes. This study provides new insight into optimizing MoS₂ catalysts for energy applications. Full article

Nitrous oxide (N₂O) is an industrial waste gas (e.g., from the production of adipic acid), which damages the ozone layer and causes the greenhouse effect. Density functional theory calculations were employed to investigate the mechanism of direct catalytic decomposition of N₂O and selective catalytic reduction (SCR) of N₂O by CO over Fe-ZSM-5 zeolites. Two stable Fe-active sites with six-membered ring structures on Fe-ZSM-5 were considered. The calculations indicate that the decomposition of N₂O is affected by the coordination environment around Fe and can occur through two reaction pathways. However, there is invariably a more considerable energy hurdle for the initiation of the second stage of N₂O decomposition. When CO participated in the reaction, it showed good reactivity and stability, the reaction energy barriers of the rate-limiting step were reduced by roughly 20.57 kcal/mol compared to the direct catalytic decomposition of N₂O. CO exhibited a superior electron-donating ability and orbital hybridization performance during the reaction, which enhanced the cyclicity of the N₂O reduction catalytic process. Our calculations confirmed the significant role of CO in N₂O reduction over Fe-ZSM-5 observed in previous studies. This study provides a valuable theoretical reference for exploring CO-SCR methods for N₂O reduction over Fe-based zeolite catalysts. Full article

The structure and performance stability of a Pt-based catalyst for propane dehydrogenation during its reaction–regeneration cycles is one of the key factors for its commercial application. A 0.3% Pt/Al₂O₃ catalyst with a sub-nanometric particle size was prepared and two different types of regeneration processes, long-term dichloroethane oxychlorination and a reaction–oxidation–oxychlorination cycle, were investigated on this catalyst. The fresh, sintered and regenerated catalyst was characterized by HAADF-STEM, CO-DRIFTS, XPS, CO chemisorption and N₂ physisorption, and its catalytic performance for propane dehydrogenation was also tested. The results show that the catalysts tend to have a similar particle size, coordination environment and catalytic performance with the extension of the regeneration time or an increase in the number of cycles in the two regeneration processes, and a common steady state could be achieved on the catalysts. This indicates that structure of the catalyst tends to approach its equilibrium state in the regeneration process, during which the utilization efficiency of Pt is maximized by increasing the dispersion of Pt and its intrinsic activity, and the structural robustness is secured. The performance of the catalyst is comparable to that of a single-atom Pt/Al₂O₃ catalyst. Full article