Catalysts, Volume 10, Issue 2 (February 2020) – 124 articles

A series of Ag/Pd/m-BiVO₄ (monoclinic) bimetallic photocatalytic materials with different loading amounts and different mass ratios of Ag and Pd were synthesized by a hydrothermal method and an NaBH₄ reduction method. The Ag/Pd/m-BiVO₄ photocatalyst with a total Ag and Pd loading of 2 wt% and an Ag-to-Pd mass ratio of 2:1 can selectively oxidize benzyl alcohol to benzaldehyde under visible light irradiation, the conversion rate was up to 89.9%, and the selectivity was greater than 99%. The conversion rate on Ag/Pd/m-BiVO₄ was higher than those on Ag/m-BiVO₄ and Pd/m-BiVO₄. The photocatalysts were characterized by X-ray powder diffraction (XRD), ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, N₂ adsorption-desorption isothermal curves (BET) and other means. The effects of different light wavelengths and light intensities were compared. Then, the effects of different alcohol derivatives on the reactions were explored. The cycle experiments proved that the Ag/Pd/m-BiVO₄ photocatalyst had good light stability and thermal stability. In addition, the capturing experiment of active species shows that the selective oxidation of benzyl alcohol is mainly accomplished through the synergistic action of h⁺, e⁻, •OH and •O₂⁻. Full article

Selective oxidation of benzyl alcohol to benzaldehyde was carried out with MoO₂ nanoparticles (MoO₂ NPs). MoO₂ NPs were synthesized by two different approaches and characterized by several techniques. The synthesis was done by a hydrothermal procedure using ethylenediamine and either Fe₂O₃ or hydroquinone. In the latter case, an additional calcination step under N₂ was performed to eliminate passivating agents at the surface of the nanoparticles. The synthesized nanocatalysts showed similar catalytic properties, being efficient catalysts in the oxidation of benzyl alcohol. High substrate conversion and product selectivity were achieved under all tested conditions. Studies were conducted using two different oxidants: tert-butyl hydroperoxide and hydrogen peroxide, in our continuous effort to obtain more efficient catalysts for more sustainable catalytic processes. When H₂O₂ was used as the oxidant, 94% yield was achieved with 100% selectivity for benzaldehyde, which was a very promising result to undergo other studies with this system. Moreover, to elucidate some aspects of the reaction mechanism, a study was conducted, and it was possible to conclude that the reaction undergoes, to some extent, through a radical mechanism with both oxidants. Full article

Ligand design in metal chemistry is a fundamental step when pursuing compounds with specific reactivity. In this paper, the functionalization of the OH group in the lateral chain of the N-heterocyclic-carbene (NHC) ligand bound to a bis-carbonyl cyclopentadienone NHC ruthenium(0) complex allowed the decoration of five generations of poly(propyleneimine) (PPIs) dendrimers with up to 64 organometallic moieties. The coupling was achieved by employing carbonyldiimidazole and the formation of carbamate linkages between dendritic peripheral NH₂ and lateral OH groups on ruthenium complexes. The synthetic procedure, chemical purification, and spectroscopic characterization of the five generations of dendrimers (3g1–5) are here described. The ruthenium-modified dendrimers were activated as catalysts in the transfer hydrogenation of the model compound 4-fluoroacetophenone in the presence of cerium ammonium nitrate as their mononuclear congeners. The catalytic activity, being similar for the five generations, shows a decrease if compared to mononuclear complexes. This detrimental effect might be ascribed to the –CH₂NH– functionalization, largely present in dendrimer skeleton and that can compete with the hydrogen transfer mechanism, but also partially to a dendritic effect caused by steric encumbrance. Full article

Electrochemical regeneration suffers from low regeneration efficiency due to side reactions like oxygen evolution, as well as oxidation of the adsorbent. In this study, electrically conducting nanocomposites, including graphene/SnO₂ (G/SnO₂) and graphene/Sb-SnO₂ (G/Sb-SnO₂) were successfully synthesized and characterized using nitrogen adsorption, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Thereafter, the adsorption and electrochemical regeneration performance of the nanocomposites were tested using methylene blue as a model contaminant. Compared to bare graphene, the adsorption capacity of the new composites was ≥40% higher, with similar isotherm behavior. The adsorption capacity of G/SnO₂ and G/Sb-SnO₂ were effectively regenerated in both NaCl and Na₂SO₄ electrolytes, requiring as little charge as 21 C mg⁻¹ of adsorbate for complete regeneration, compared to >35 C mg⁻¹ for bare graphene. Consecutive loading and anodic electrochemical regeneration cycles of the nanocomposites were carried out in both NaCl and Na₂SO₄ electrolytes without loss of the nanocomposite, attaining high regeneration efficiencies (ca. 100%). Full article

Zirconia has recently been used as an efficient catalyst in the conversion of syngas. The crystalline phases of ZrO₂ in ZrO₂/HZSM-5 bi-functional catalysts have important effects on C–O activation and C–C coupling in converting syngas into aromatics and been investigated in this work. Monoclinic ZrO₂ (m-ZrO₂) and tetragonal ZrO₂ (t-ZrO₂) were synthesized by hydrothermal and chemical precipitation methods, respectively. The results of in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTs) revealed that there were more active hydroxyl groups existing on the surface of m-ZrO₂, and CO temperature programmed desorption (CO-TPD) results indicated that the CO adsorption capacity of m-ZrO₂ was higher than that of t-ZrO₂, which can facilitate the C–O activation of m-ZrO₂ for syngas conversion compared to that of t-ZrO₂. And the CO conversion on the m-ZrO₂ catalyst was about 50% more than that on the t-ZrO₂ catalyst. ³¹P and ¹³C magic angle spinning nuclear magnetic resonance (MAS NMR) analysis revealed a higher acid and base density of m-ZrO₂ than that of t-ZrO₂, which enhanced the C–C coupling. The selectivity to CH₄ on the m-ZrO₂ catalyst was about 1/5 of that on the t-ZrO₂ catalyst in syngas conversion. The selectivity to C₂₊ hydrocarbons over m-ZrO₂ or t-ZrO₂ as well as the proximity of the ZrO₂ sample and HZSM-5 greatly affected the further aromatization in converting syngas into aromatics. Full article

High-stability, high-efficiency, and low-cost solar photoelectrochemical (PEC) water splitting has great potential for hydrogen-energy applications. Here, we report on gold/titanium dioxide (Au/TiO₂) nanofiber structures grown directly on a conductive indium tin oxide substrate, and used as photoelectrodes in PEC cells for hydrogen generation. The titanium dioxide nanofibers (TiO₂ NFs) are synthesized using electrospinning, and are surface-modified by the deposition of gold nanoparticles (Au NPs) using a simple photoreduction method. The structure and morphology of the materials were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The surface plasmon resonance (SPR) of the Au NPs was investigated by ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy. The PEC properties of the as-prepared photoelectrodes were measured. The obtained photoconversion efficiency of 0.52% under simulated-sunlight illumination by a 150 W xenon lamp of the Au/TiO₂ NFs structure with 15 min UV irradiation for Au NP deposition was the highest value from comparable structures. Working photoelectrode stability was tested, and the mechanism of the enhanced PEC performance is discussed. Full article

Ene-reductases (ERs) belonging to the old yellow enzyme (OYE) family have been thoroughly investigated for the stereospecific reduction of activated prochiral C=C double bonds. In this work, OYE3 was immobilized both by covalent binding on glyoxyl-agarose (OYE3-GA), and by affinity-based adsorption on EziG^TM particles (OYE3-EziG). The immobilized OYE3-GA was demonstrated to be active (activity recovery = 52%) and to retain almost 100% of its activity under the enzymatic assay conditions (50 mM phosphate buffer pH 7, 28 °C) for six days, whereas the activity of the non-immobilized enzyme dropped to 50% after two days. In the case of EziG^TM, the highest activity recovery (54%) was achieved by using the most hydrophilic carrier (EziG^TM Opal) that was selected for the full characterization of this type of enzyme preparation (stability, recycling, re-use, enzyme leakage). OYE3-EziG was slightly less stable than OYE3-GA under the same experimental conditions. OYE3-GA could be recycled and re-used for up to 12 reaction cycles in the bioreduction of α-methyl-trans-cinnamaldehyde; after 12 runs, the highest conversion achieved was 40%. In the case of the co-immobilized OYE3/GDH-EziG, the conversion dropped to 56% after two reaction cycles. No enzyme leakage was detected over 48 h for both OYE3-GA and OYE3/GDH-EziG (50 mM phosphate buffer pH 7, 28 °C). These seed results pave the way for a true optimization of the immobilization of OYE3, as well as for the use of immobilized OYE3 for preparative applications both in batch and continuous flow conditions. Full article

Sulfonated carbon-based catalysts have been identified as promising solid acid catalysts, and petroleum coke (petcoke), a byproduct of the oil industry, is a potential feedstock for these catalysts. In this study, sulfur-containing (6.5 wt%) petcoke was used as a precursor for these catalysts through direct functionalization (i.e., without an activation step) with nitric acid to access the inherent sulfur. Catalysts were also prepared using sulfuric acid and a mixture of nitric and sulfuric acid (1:3 vol ratio). Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and titration were used to identify and quantify the acid sites. The activities of the prepared catalysts were determined for the esterification of octanoic acid with methanol. Petcoke had few −SO₃H groups, and correspondingly no catalytic activity for the reaction. All acid treatments increased the number of −SO₃H groups and promoted esterification. Treatment with nitric acid alone resulted in the oxidation of the inherent sulfur in petcoke to produce ~0.7 mmol/g of strong acid sites and a total acidity of 5.3 mmol/g. The acidity (strong acid and total) was lower with sulfuric acid treatment but this sample was more active for the esterification reaction (TOF of 31 h⁻¹ compared to 7 h⁻¹ with nitric acid treatment). Full article

Calycosin-7-O-β-D-glucoside (Cy7G) is one of the principal components of Radix astragali. This isoflavonoid glucoside is regarded as an indicator to assess the quality of R. astragali and exhibits diverse pharmacological activities. In this study, uridine diphosphate-dependent glucosyltransferase (UGT) UGT88E18 was isolated from Glycine max and expressed in Escherichia coli. Recombinant UGT88E18 could selectively and effectively glucosylate the C7 hydroxyl group of calycosin to synthesize Cy7G. A one-pot reaction by coupling UGT88E18 to sucrose synthase (SuSy) from G. max was developed. The UGT88E18–SuSy cascade reaction could recycle the costly uridine diphosphate glucose (UDPG) from cheap sucrose and catalytic amounts of uridine diphosphate (UDP). The important factors for UGT88E18–SuSy cascade reaction, including UGT88E18/SuSy ratios, different temperatures, and pH values, different concentrations of dimethyl sulfoxide (DMSO), UDP, sucrose, and calycosin, were optimized. We produced 10.5 g L⁻¹ Cy7G in the optimal reaction conditions by the stepwise addition of calycosin. The molar conversion of calycosin was 97.5%, with a space–time yield of 747 mg L⁻¹ h⁻¹ and a UDPG recycle of 78 times. The present study provides a new avenue for the efficient and cost-effective semisynthesis of Cy7G and other valuable isoflavonoid glucosides by UGT–SuSy cascade reaction. Full article

Bi₂₄O₃₁Br₁₀ microcrystals composed of nanobelts and nanosheets with exposed (30-4) and (117) facets were synthesized by a simple hydrothermal method. The desired morphology and facets were obtained by adjusting the pH of the reaction system. Bi₂₄O₃₁Br₁₀ nanobelts (BOB-NBs) with dominant (30-4) exposed facets were used for the photocatalytic degradation of tetracycline hydrochloride under visible light irradiation, with a degradation efficiency of up to 91% after 60 min of irradiation. The BOB-NBs possessed a higher charge separation and transfer efficiency, and showed less charge carrier recombination compared to the Bi₂₄O₃₁Br₁₀ nanosheets (BOB-NSs), ascribed to a cooperative effect between the internal electric fields and surface active sites. A higher photocurrent response (2.6 times higher) was observed for BOB-NBs (12.8 μA cm⁻²) compared to that of BOB-NSs (4.9 μA cm⁻²). These findings are directional for a comprehensive understanding of the influence of the crystal facets of Bi₂₄O₃₁Br₁₀ microcrystals on their photocatalytic activity and could help to guide the future design of high-performance photocatalytic materials. Full article

Activated carbon (AC) was synthesized with various weight ratios of manganese dioxide (MO) through a simple hydrothermal approach. The electrochemical performance of the synthesized activated carbon/MnO₂ composites was investigated. The effect of the activated carbon/MnO₂ (AM) ratio on the electrochemical properties of the activated carbon/MnO₂ composites and the pore structure was also examined. The results show that the specific capacitance of the activated carbon material has been improved after the addition of MO. The as-synthesized composite material exhibits specific capacitance of 60.3 F g⁻¹ at 1 A g⁻¹, as well as stable cycle performance and 99.6% capacitance retention over 5000 cycles. Full article

In this study, the effect of a mechanocatalytic pretreatment on the structure of willow and sugar release from pretreated willow was explored. In the mechanocatalytic approach, the pretreatment consists of solvent-free impregnation with sulfuric acid and a mechanical treatment with ball milling. Willow sawdust and pretreated samples were analyzed with field emission scanning electron microscope and X-ray diffraction. The products in the sugar solution were determined as the total reducing sugars with the 3,5-dinitrosalicylic acid method and monosaccharides with capillary electrophoresis. According to the results, milling increased the sugar production, depending on the sulfuric acid load. The milling parameters, such as the rotation speed of the mill, the catalyst-to-willow ratio, and the milling time influenced the amount of sugars in the hydrolysate and the composition of the sugar solution produced. Changes were observed in the surface of the willow particles as well as changes in the crystalline structure. Glucose and xylose yields increased after 15 min of milling and reached their maximum level after 45 min of milling with the 0.5 mmol/g sulfuric acid load. Full article

Ene reductases enable the asymmetric hydrogenation of activated alkenes allowing the manufacture of valuable chiral products. The enzymes complement existing metal- and organocatalytic approaches for the stereoselective reduction of activated C=C double bonds, and efforts to expand the biocatalytic toolbox with additional ene reductases are of high academic and industrial interest. Here, we present the characterization of a novel ene reductase from Paenibacillus polymyxa, named Ppo-Er1, belonging to the recently identified subgroup III of the old yellow enzyme family. The determination of substrate scope, solvent stability, temperature, and pH range of Ppo-Er1 is one of the first examples of a detailed biophysical characterization of a subgroup III enzyme. Notably, Ppo-Er1 possesses a wide temperature optimum (T_opt: 20–45 °C) and retains high conversion rates of at least 70% even at 10 °C reaction temperature making it an interesting biocatalyst for the conversion of temperature-labile substrates. When assaying a set of different organic solvents to determine Ppo-Er1′s solvent tolerance, the ene reductase exhibited good performance in up to 40% cyclohexane as well as 20 vol% DMSO and ethanol. In summary, Ppo-Er1 exhibited activity for thirteen out of the nineteen investigated compounds, for ten of which Michaelis–Menten kinetics could be determined. The enzyme exhibited the highest specificity constant for maleimide with a k_cat/K_M value of 287 mM⁻¹ s⁻¹. In addition, Ppo-Er1 proved to be highly enantioselective for selected substrates with measured enantiomeric excess values of 92% or higher for 2-methyl-2-cyclohexenone, citral, and carvone. Full article

Due to their adsorbent, ion exchange and catalytic properties zeolites are suitable for a variety of applications. We report on the photocatalytic activity of a readily available and inexpensive natural zeolite clinoptilolite (Z) containing SnO₂ (Sn-Z). The Sn-Z samples with 3–15 wt. % of Sn were prepared by using a precipitation–deposition method. Powder X-ray diffraction analysis showed that the zeolite structure was unaffected by the introduction of the Sn-phase. Diffuse reflectance UV/VIS spectra of the Sn-Z samples confirmed the presence of SnO₂ and X-Ray absorption spectroscopy analyses suggested that the SnO₂ particles mainly resided on the surface of the clinoptilolite, while ATR-FTIR analysis gave some clues that part of the SnO₂ phase was incorporated in the pores of the zeolite. The presence of SnO₂ in Sn-Z increased both adsorption capacity and photocatalytic performance which could be partially explained by higher surface area and partially with an increased negative potential of the surface. Adsorption and total degradation of methylene blue (MB) for the Sn-Z with the highest amount of Sn (15 wt.%) was about 30% and 45%, respectively, suggesting a synergetic effect between SnO₂ and the clinoptilolite lattice. Reusability tests showed that these catalysts present a promising material for water purification. Full article

N-Hydroxyphthalimide was immobilized via ester bond on commercially available silica gel (SiOCONHPI) and then coated with various ionic liquids containing dissolved CoCl₂ ([email protected]₂@IL). New catalysts were characterized by means of FT IR spectroscopy, elemental analysis, SEM and TGA analysis and used in ethylbenzene oxidation with oxygen under mild solvent-free conditions (80 °C, 0.1 MPa). High catalytic activity of SiOCONHPI was proved. In comparison to a non-catalytic reaction, a two-fold increase in conversion of ethylbenzene was observed (from 4.7% to 8.6%). Coating of SiOCONHPI with [bmim][OcOSO₃], [bmim][Cl] and [bmim][CF₃SO₃] containing CoCl₂ enabled to increase the catalytic activity in relation to systems in which IL and CoCl₂ were added directly to reaction mixture. The highest conversion of ethylbenzene was obtained while [email protected]₂@[bmim][OcOSO₃] were used (12.1%). Catalysts recovery and reuse was also studied. Full article

Single doping and co-doping of N and Ag on TiO₂ were successfully prepared by using an in-situ solvothermal method and their structural properties and chemical compositions were characterized. The results indicated that all photocatalysts displayed in TiO₂ anatase crystal phase, and a small mesoporous structure was observed in the doped materials. The main roles of N and Ag on the property and photocatalytic activity of TiO₂ were different. The N doping has significantly enhanced homogenous surface morphology and specific surface area of the photocatalyst. While Ag doping was narrowing the band gap energy, extending light absorption toward a visible region by surface plasmon resonance as well as delaying the recombination rate of electron and hole of TiO₂. The existence of N in TiO₂ lattice was observed in two structural linkages such as substitutional nitrogen (Ti-O-N) and interstitial nitrogen (O-Ti-N). Silver species could be in the form of Ag⁰ and Ag₂O. The photocatalytic performance of the photocatalysts coated on stainless steel mesh was investigated by the degradation of aqueous MB and gas phase NH₃ under visible LED light illumination for three recycling runs. The highest photocatalytic activity and recyclability were reached in 5% N/Ag-TiO₂ showing the efficiency of 98.82% for methylene blue (MB) dye degradation and 37.5% for NH₃ removal in 6 h, which was 2.7 and 4.3 times, respectively. This is greater than that of pure TiO₂. This was due to the synergistic effect of N and Ag doping. Full article

Highly porous cellular material (α-Al₂O₃-HPCM) support was synthesized by the template method. Highly porous support was used for the synthesis of the catalyst. A thin secondary layer with 25–30 μ thick γ-Al₂O₃ and zeolite Y was applied on the α-Al₂O₃-HPCM surface ((γ-Al₂O₃ (85%)-zeolite Y (15%))/α-Al₂O₃-HPCM). The catalyst based on the highly porous support was tested in a process of decreasing oil viscosity. The catalyst in the form of cylindrical granules and a thermal process of decreasing oil viscosity without the catalyst were used as the basis for comparison. α-Al₂O₃-HPCM in the catalyst provides low-quantity pores (d < 10 nm) and a quantity of general acid centers compared with the granular catalyst. On the other hand, it shows a more significant oil viscosity decrease (from 2500 to 41 cPs) and a low rate of gas generation (137 mL/h) for the catalyst with highly porous support. A high oil fraction was observed in the presence of the (γ-Al₂O₃-zeolite Y)/α-Al₂O₃-HPCM compared to the granular catalyst. The presence of large transport cells (pores) 1500–2000 μ for the catalyst based on highly porous support allowed a work period four times longer than that of experiment only with temperature without catalysts. Full article

This study examined the removal of natural organic substances (humic acids-HA, and fulvic acids-FA) from model solutions using photocatalysis and ultrafiltration. The effect of two nano titanium dioxide types (P25 and P90) with different active surface areas and two UV lamps (low-pressure and medium-pressure) on the effectiveness of FA and HA removal during photocatalysis was tested. An integrated photocatalytic + ultrafiltration system was also analyzed to determine the effectiveness of FA and HA removal and the changes in the relative permeate flux (Ultrafiltration Membrane Fouling-UF). We observed that photocatalysis using the P90 nano titanium dioxide was more efficient than the P25 due to the larger surface area (2×). The decomposition of organic substances proceeded efficiently up to 30 min of solution exposure, and the use of a medium-pressure lamp accelerated compound decomposition relative to the low-pressure lamp. The applied photocatalysis + ultrafiltration system was characterized by a high degree of FA removal while improved hydraulic efficiency was observed during ultrafiltration. Full article

The oxidation of methanol is studied at TiO₂-supported Pt electrodes of varied high surface area carbon content (in the 30-5% w/w range) and C÷Ti atom ratio (in the 3.0-0.4 ratio). The Pt-TiO₂ catalyst is prepared by a photo-deposition process and C nanoparticles (Vulcan XC72R) are added by simple ultrasonic mixing. The optimum C÷Ti atom ratio of the prepared catalyst for methanol electro-oxidation is found to be 1.5, resulting from the interplay of C properties (increased electronic conductivity and methanol adsorption), those of TiO₂ (synergistic effect on Pt and photo-activity), as well as the catalyst film thickness. The intrinsic catalytic activity of the best Pt-TiO₂/C catalyst is better than that of a commercial Pt/C catalyst and could be further improved by nearly 25% upon UV illumination, whose periodic application can also limit current deterioration. Full article

Since the late 1980s, the scientific community has been attracted to microwave energy as an alternative method of heating, due to the advantages that this technology offers over conventional heating technologies. In fact, differently from these, the microwave heating mechanism is a volumetric process in which heat is generated within the material itself, and, consequently, it can be very rapid and selective. In this way, the microwave-susceptible material can absorb the energy embodied in the microwaves. Application of the microwave heating technique to a chemical process can lead to both a reduction in processing time as well as an increase in the production rate, which is obtained by enhancing the chemical reactions and results in energy saving. The synthesis and sintering of materials by means of microwave radiation has been used for more than 20 years, while, future challenges will be, among others, the development of processes that achieve lower greenhouse gas (e.g., CO₂) emissions and discover novel energy-saving catalyzed reactions. A natural choice in such efforts would be the combination of catalysis and microwave radiation. The main aim of this review is to give an overview of microwave applications in the heterogeneous catalysis, including the preparation of catalysts, as well as explore some selected microwave assisted catalytic reactions. The review is divided into three principal topics: (i) introduction to microwave chemistry and microwave materials processing; (ii) description of the loss mechanisms and microwave-specific effects in heterogeneous catalysis; and (iii) applications of microwaves in some selected chemical processes, including the preparation of heterogeneous catalysts. Full article

Light olefins including ethylene, propylene and butylene are important building blocks in petrochemical industries to produce various chemicals such as polyethylene, polypropylene, ethylene oxide and cumene. Traditionally, light olefins are produced via a steam cracking process operated at an extremely high temperature. The catalytic conversion, in which zeolites have been widely used, is an alternative pathway using a lower temperature. However, conventional zeolites, composed of a pure microporous structure, restrict the diffusion of large molecules into the framework, resulting in coke formation and further side reactions. To overcome these problems, hierarchical zeolites composed of additional mesoporous and/or macroporous structures have been widely researched over the past decade. In this review, the recent development of hierarchical zeolite nanosheets and nanoparticle assemblies together with opening up their applications in various light olefin productions such as catalytic cracking, ethanol dehydration to ethylene, methanol to olefins (MTO) and other reactions will be presented. Full article

Sulfite and heavy metals are crucial pollutants in the slurry produced by flue gas desulfurization. In this study, a novel cobalt-based activated carbon fiber (Co-ACFs) catalyst-adsorbent was synthesized using an impregnation method; this bifunctional catalyst-adsorbent was used in wet magnesia desulfurization for the simultaneous catalytic oxidation of magnesium sulfite and uptake of heavy metal (Hg²⁺, Cd²⁺, and Ni²⁺) ions. The morphology and surface chemistry of ACFs before and after cobalt loading were investigated using various characterization methods. The kinetics on catalytic oxidation of magnesium sulfite was investigated, and the effects of operation conditions on the simultaneous adsorption capacity of heavy metals were examined. Relative to a non-catalysis material, the 40% Co-ACFs material increased the oxidation rate of magnesium sulfite by more than five times. The Langmuir model can describe the adsorption behavior of Co-ACFs on Hg²⁺, Cd²⁺, and Ni²⁺, indicating that the simultaneous uptake of heavy metals is a single-layer adsorption process. The maximum adsorption capacities for Hg²⁺, Cd²⁺, and Ni²⁺ are 333.3, 500, and 52.6 mg/g, respectively. A pseudo-second-order model confirmed that the removal of heavy metals is controlled by the chemisorption process. Full article

Hydrothermal and co-precipitation methods were studied as two different methods for the synthesis of CeO₂nanocatalysts. Co/CeO₂ catalysts supported by 2, 4, 6, or 8wt% Co were further synthesized through impregnation and the performance of the catalytic oxidation of CO has been investigated. The highest specific surface area and the best catalytic performance was obtained by the catalyst 4wt% Co/CeO₂ with the CeO₂ support synthesized by the hydrothermal method (4% Co/CeO₂-h), which yielded 100% CO conversion at 130 °C. The formation of CeO₂ nanoparticles was confirmed by TEM analysis. XRD and SEM-EDX mapping analyses indicated that CoO_x is highly dispersed on the 4% Co/CeO₂-h catalyst surface. H₂-TPR and O₂-TPD results showed that 4% Co/CeO₂-h possesses the best redox properties and the highest amount of chemically adsorbed oxygen on its surface among all tested catalysts. Raman and XPS spectra showed strong interactions between highly dispersed Co²⁺ active sites and exposed Ce³⁺ on the surface of the CeO₂ support, resulting in the formation of the strong redox cycle Ce⁴⁺ + Co²⁺↔ Ce³⁺ + Co³⁺.This may explain that 4% Co/CeO₂-h exhibited the best catalytic activity among all tested catalysts. Full article

Dry reforming of methane (DRM) was studied in the light of Ni supported on 8%PO₄ + ZrO₂ catalysts. Cerium was used to modify the Ni active metal. Different percentage loadings of Ce (1%, 1.5%, 2%, 2.5%, 3%, and 5%) were tested. The wet incipient impregnation method was used for the preparation of all catalysts. The catalysts were activated at 700 °C for ½ h. The reactions were performed at 800 °C using a gas hourly space velocity of 28,000 mL (h·gcat)⁻¹. X-ray diffraction (XRD), N₂ physisorption, hydrogen temperature programmed reduction (H₂-TPR), temperature programmed oxidation (TPO), temperature programmed desorption (TPD), and thermogravimetric analysis (TGA) were used for characterizing the catalysts. The TGA analysis depicted minor amounts of carbon deposition. The CO₂-TPD results showed that Ce enhanced the basicity of the catalysts. The 3% Ce loading possessed the highest surface area, the largest pore volume, and the greatest pore diameter. All the promoted catalysts enhanced the conversions of CH₄ and CO₂. Among the promoted catalysts tested, the 10Ni + 3%Ce/8%PO₄ + ZrO₂ catalyst system operated at 1 bar and at 800 °C gave the highest conversions of CH₄ (95%) and CO₂ (96%). The stability profile of Cerium-modified catalysts (10%Ni/8%PO₄ + ZrO₂) depicted steady CH₄ and CO₂ conversions during the 7.5 h time on stream. Full article

In this work, two kinds of catalyst called monometallic Palladium (Pd) and a bimetallic of Pd-Iron (Fe) were synthesised using aluminum oxide (Al₂O₃) as the supported material via the wet impregnate method. A monometallic catalyst (0.5% Pd/Al₂O₃) named Pd cat was used as control. For the bimetallic catalyst, ratios of Pd to Fe were varied, and included 0.38% Pd–0.12% Fe (PF1), 0.25% Pd–0.25% Fe (PF2), and 0.12% Pd–0.38% Fe (PF3). The catalysts were characterised to investigate physical properties such as the surface area, pore size, porosity, and pore size distribution including their composition by Brunauer–Emmett–Teller (BET) surface area, Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD). Subsequently, all catalysts were applied for biofuels production in terms of green diesel/kerosene/gasoline from palm oil via a hydrocracking reaction. The results showed that the loading of Fe to Pd/Al₂O₃ could improve the active surface area, porosity, and pore diameter. Considering the catalytic efficiency for the hydrocracking reaction, the highest crude biofuel yield (94.00%) was obtained in the presence of PF3 catalyst, while Pd cat provided the highest refined biofuel yield (86.00%). The largest proportion of biofuel production was green diesel (50.00–62.02%) followed by green kerosene (31.71–43.02%) and green gasoline (6.10–8.11%), respectively. It was clearly shown that the Pd-Fe bimetallic and Pd monometallic catalysts showed potential for use as chemical catalysts in hydrocracking reactions for biofuel production. Full article

Geopolymer (GP) spheres made from coal fly ash (FA) and rice hull ash (RHA) waste products are utilized as both support matrix and dopant applied to titania (TiO₂) photocatalyst for organic dye degradation in wastewater. Processing of FA and RHA via suspension-solidification method resulted in GP spheres with nanoporous morphology. The nanocrevices enabled low-energy sol-gel TiO₂ coating technique because they served as anchoring sites on the geopolymer surface that favored rigidity and larger surface area. The GP-TiO₂ system has been characterized by infrared spectroscopy, X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Diffuse reflectance spectroscopy revealed a narrowing of the GP-TiO₂ system optical band gap due to the interaction of metal dopants contained in RHA and FA with TiO₂, thus making the GP-TiO₂ system a visible-light-active photocatalyst, as confirmed by methylene blue dye degradation measured through UV-Vis spectroscopy. Full article

In this work, the design and manufacture of graphite paste (Gr) electrodes is carried out, including N-octylpyridinium hexafluorophosphate (OPyPF₆) ionic liquid (IL) as binder and modification with Co-octaethylporphyrin (Co), in order to study the hydrogen evolution reaction (HER) in the absence and presence of light. The system is characterized by XRD and FESEM-EDX (Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy), confirming the presence of all the components of the system in the electrode surface. The studies carried out in this investigation confirm that a photoelectrocatalytic system towards HER is obtained. The system is stable, efficient and easy to prepare. Through cyclic voltammetry and electrochemical impedance spectroscopy, was determined that these electrodes improve their electrochemical and electrical properties upon the addition of OPyPF₆. These effects improve even more when the systems are modified with Co porphyrin. It is also observed that when the systems are irradiated at 395 nm, the redox process is favored in energy terms, as well as in its electrical properties. Through gas chromatography, it was determined that the graphite paste electrode in the presence of ionic liquid and porphyrin (Gr/IL/Co) presents a high turnover number (TON) value (6342 and 6827 in presence of light) in comparison to similar systems reported. Full article

Cosmetics and other daily care products contain titanium(IV) oxide (titania). Since multiple risk factors can increase the chance of developing cancer, an evaluation of titania safety has become a matter of concern in recent times. However, it should be pointed out that titania as an efficient photocatalyst has been also applied for inactivation of various pathogens, environmental purification and energy conversion, which might result in significant improvement of human life. Therefore, it is worth considering titania not only as a possible cancer initiator, but also as an efficient solution against cancer cells. Accordingly, in this study, the effect of commercial titania photocatalyst P25 (Degussa/Evonik) on breast adenocarcinoma MCF7 cells (ATCC^® HTB-22™, breast adenocarcinoma cell line from human) has been investigated. The cells were treated with titania at doses of 10, 30, and 50 µg/mL under UVA/vis irradiation and in the dark. The significant morphological alterations in living cells were observed for larger doses of titania, such as changes in the shape and the size of cells, the deviation from the normal structure, and an increase in cells’ mortality. Moreover, the effect was significantly higher under irradiation than in the dark confirming strong photocatalytic activity of titania P25. In contrast, the lowest dose of titania (10 µg/mL) did not exhibit a significant impact on MCF7 cells, similarly to the nontreated cells. Accordingly, it has been proposed that locally applied titania might be considered for a cancer therapy after necessary in vivo tests to estimate any possibilities of side effects. Full article

The development of solid acid catalysts, especially based on metal oxides and different magnetic nanoparticles, gained much awareness recently as a result of the development of different nano-based materials. Solid acid catalysts based on metal oxides are promising for the (trans)esterification reactions of different oils and waste materials for biodiesel production. This review gives a brief overview of recent developments in various solid acid catalysts based on different metal oxides, such as zirconia, zinc, titanium, iron, tungsten, and magnetic materials, where the catalysts are optimized for various reaction parameters, such as the amount of catalyst, molar ratio of oil to alcohol, reaction time, and temperature. Furthermore, yields and conversions for biodiesel production are compared. Such metal-oxide-based solid acid catalysts provide more sustainable, green, and easy-separation synthesis routes with high catalytic activity and reusability than traditionally used catalysts. Full article