Catalysts, Volume 10, Issue 5 (May 2020) – 129 articles

SBA-15 materials as-synthesized and impregnated with Ag nanoparticles were applied to perform adsorptive desulfurization of real diesel fuel. High-angle annular dark-field scanning transmission electron microscopy and field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (HAADF-STEM-EDX and FESEM-EDX) and X-ray photoelectron spectroscopy (XPS) results confirmed that there is uniform distribution of Ag nanodomains on the surface and in the channels of a 2AgSBA-15 (2% Ag) sample. The interaction between sulfur compounds and adsorbent mainly occurred via π-complexation mechanisms, as observed via XPS and equilibrium data. The kinetic results for 2AgSBA-15 were better fitted to the pseudo-second-order model (R² > 0.9999), indicating that the determining step of the adsorptive process is chemisorption, whereas the equilibrium results were better fitted to the Langmuir model (R² > 0.9994), thus indicating that the adsorption occurs on the adsorbent surface monolayer with significant adsorption capacity (q_m = 20.30 mgS/g), approximately two times greater than that observed for pure SBA-15. The mean desulfurization reached by the adsorbents was up to 86.8% for six recycling steps. Full article

Dry reforming of methane (DRM) involves the conversion of CO₂ and CH₄, the most important greenhouse gases, into syngas, a stoichiometric mixture of H₂ and CO that can be further processed via Fischer–Tropsch chemistry into a wide variety of products. However, the devolvement of the coke resistant catalyst, especially at high pressures, is still hampering commercial applications. One of the relatively new approaches for the synthesis of metal nanoparticle based catalysts comprises the use of metal-organic frameworks (MOFs) as catalyst precursors. In this work we have explored MOF-74/CPO-27 MOFs as precursors for the synthesis of Ni, Co and bimetallic Ni-Co metal nanoparticles. Our results show that the bimetallic system produced through pyrolysis of a Ni-Co@CMOF-74 precursor displays the best activity at moderate pressures, with stable performance during at least 10 h at 700 °C, 5 bar and 33 L·h⁻¹·g⁻¹. Full article

Under the acyclic diene metathesis (ADMET) reaction condition, the C3-vinyl groups of cinchona alkaloids readily react with each other to form a C-C bond. A novel type of cinchona alkaloid polymers was synthesized from dimeric cinchona squaramides using the Hoveyda-Grubbs’ second-generation catalysts (HG₂) by means of ADMET reaction. The chiral polymers, containing cinchona squaramide moieties in their main chains, were subsequently employed as catalysts for the enantioselective Michael reaction to give the corresponding chiral adducts in high yields with excellent enantioselectivity and diastereoselectivity. Both enantiomers from the asymmetric Michael reaction were distinctively prepared while using the polymeric catalysts, possessing pseudoenantiomeric structures. The catalysts were readily recovered from the reaction mixture and recycled several times due to the insolubility of the cinchona-based squaramide polymers. Full article

Developing a novel ammonia synthesis process from N₂ and H₂ is of interest to the catalysis and hydrogen research communities. γ-Alumina-supported nickel was determined capable of serving as an efficient catalyst for ammonia synthesis using nonthermal plasma under atmospheric pressure without heating. The catalytic activity was almost unrelated to the crystal structure and the surface area of the alumina carrier. The activity of Ni/Al₂O₃ was quantitatively compared with that of Fe/Al₂O₃ and Ru/Al₂O₃, which contained active metals for the conventional Haber–Bosch process. The activity sequence was Ni/Al₂O₃ > Al₂O₃ > Fe/Al₂O₃ > no additive > Ru/Al₂O₃, surprisingly indicating that the loading of Fe and Ru decreased the activity of Al₂O₃. The catalytic activity of Ni/Al₂O₃ was dependent on the amount of loaded Ni, the calcination temperature, and the reaction time. XRD, visual, and XPS observations of the catalysts before the plasma reaction indicated the generation of NiO and NiAl₂O₄ on Al₂O₃, the latter of which was generated upon high-temperature calcination. The NiO species was readily reduced to Ni metal in the plasma reaction, whereas the NiAl₂O₄ species was difficult to reduce. The catalytic behavior could be attributed to the production of fine Ni metal particles that served as active sites. The P_N2/P_H2 ratio dependence and rate constants of formation and decomposition of ammonia were finally determined for 5.0 wt% Ni/Al₂O₃ calcined at 773 K. The ammonia yield was 6.3% at an applied voltage of 6.0 kV, a residence time of reactant gases of 0.12 min, and P_H2/P_N2 = 1. Full article

The aerobic oxidation of cyclohexene was done using the heterometallic metal organic frameworks (MOFs) {[La₂Cu₃(μ-H₂O)(ODA)₆(H₂O)₃]⋅3H₂O}_n (LaCuODA)) (1) and {[La₂Co₃(ODA)₆(H₂O)₆]∙12H₂O}_n (LaCoODA) (2) as catalysts, in solvent free conditions (ODA, oxydiacetic acid). After 24 h of reaction, the catalytic system showed that LaCoODA had a better catalytic performance than that of LaCuODA (conversion 85% and 67%). The structures of both catalysts were very similar, showing channels running along the c axis. The physicochemical properties of both MOFs were determined to understand the catalytic performance. The Langmuir surface area of LaCoODA was shown to be greater than that of LaCuODA, while the acid strength and acid sites were greater for LaCuODA. On the other hand, the redox potential of the active sites was related to Co^II/Co^III in LaCoODA and Cu^II/Cu^I in LaCuODA. Therefore, it is concluded that the Langmuir surface area and the redox potentials were more important than the acid strength and acid sites of the studied MOFs, in terms of the referred catalytic performance. Finally, the reaction conditions were also shown to play an important role in the catalytic performance of the studied systems. Especially, the type of oxidant and the way to supply it to the reaction medium influenced the catalytic results. Full article

The interesterification reaction of egg-yolk phosphatidylcholine (PC) with ethyl ester of 3,4-dimethoxycinnamic acid (E3,4DMCA) catalyzed by Novozym 435 in hexane as a reaction medium was shown to be an effective method for the synthesis of corresponding structured O-methylated phenophospholipids. The effects of substrate molar ratios, time of the reaction and enzyme load on the process of incorporation of 3,4DMCA into PC were evaluated by using the experimental factorial design of three factors and three levels. The results showed that a substrate molar ratio is a crucial variable for the maximization of the synthesis of 3,4-dimethoxycinnamoylated phospholipids. Under optimized parameters of 1/10 substrate molar ratio PC/E3,4DMCA, enzyme load 30% (w/w), hexane as a medium and incubation time of 3 days, the incorporation of aromatic acid into phospholipid fraction reached 21 mol%. The modified phosphatidylcholine (3,4DMCA-PC) and modified lysophosphatidylcholine (3,4DMCA-LPC) were obtained in isolated yields of 3.5% and 27.5% (w/w), respectively. The developed method of phosphatidylcholine interesterification is the first described in the literature dealing with 3,4DMCA and allows us to obtain new O-methylated phenophospholipids with potential applications as food additives or nutraceuticals with pro-health activity. Full article

All modern diesel vehicles in Europe are equipped with diesel particulate filters (DPFs) and their particle number (PN) emissions at the tailpipe are close to ambient air levels. After the Dieselgate scandal for high NO_x emissions of diesel vehicles on the road, the high PN emissions during regeneration events are on the focus. The PN emissions of a diesel vehicle on the road and in the laboratory with or without regeneration events were measured using systems with evaporation tubes and catalytic strippers and counters with lower sizes of 23, 10 and 4 nm. The tests showed significant PN levels only during engine cold starts with a big fraction of sub-23 nm particles during the first minute. After the first seconds the sub-23 nm fraction was negligible. Urea injection at the selective catalytic reduction (SCR) for NO_x system did not affect the PN levels and the sub-23 nm fraction. The emissions during regeneration events were higher than the PN limit, but rapidly decreased 2-3 orders of magnitude below the limit after the regeneration. Artificially high sub-10 nm levels were seen during the regeneration (volatile artifact) at the system with the evaporation tube. The regenerations were forced every 100–350 km and the overall emissions including the regeneration events were two to four times lower than the current laboratory PN limit. The results of this study confirmed the efficiency of DPFs under laboratory and on-road driving conditions. Full article

In this study, titania nanoparticles were obtained using the microwave-assisted technique. Moreover, different surfactants (PEG (M_n = 400), Pluronic P123 and Triton X−100) were used during the synthesis in order to determine their impact on the crystallinity and morphology of the final products. Subsequently, techniques such as XRD, SEM and TEM (performed in high contrast and high-resolution mode), diffuse reflectance spectroscopy (DRS), low temperature N₂ sorption (BET model), FTIR and TGA were carried out. Based on the crystallinity analysis of the obtained materials, it was established that the addition of surfactants results in greater (PEG and Triton X−100) or smaller (Pluronic P123) average crystallite size. The main purpose of this study was to use the synthesized nanomaterials in the photodegradation process (in the UV light range) of the model organic pollutants – phenol (20 mg/L) and etodolac (15 mg/L). Furthermore, it was also pointed out that the dye-sensitized solar cells can be a second application for the synthesized titania nanomaterials. The photo-oxidation and photovoltaic tests have shown that the titanium dioxide obtained using the surfactant-assisted microwave method is characterized not only by better photodegradation efficiency of phenol and etodolac, but also by higher photocurrent density compared to the reference titania samples—the pristine TiO₂ and commercial P25. Full article

The aim of this study was to investigate the effects of aluminum (Al) or selenium (Se) on the “primary” antioxidant defense system enzymes (superoxide dismutase, catalase, and glutathione reductase) in cells of mouse brain and liver after long-term (8-week) exposure to drinking water supplemented with AlCl₃ (50 mg or 100 mg Al/L in drinking water) or Na₂SeO₃ (0.2 mg or 0.4 mg Se/L in drinking water). Results have shown that a high dose of Se increased the activities of superoxide dismutase and catalase in mouse brain and liver. Exposure to a low dose of Se resulted in an increase in catalase activity in mouse brain, but did not show any statistically significant changes in superoxide dismutase activity in both organs. Meanwhile, the administration of both doses of Al caused no changes in activities of these enzymes in mouse brain and liver. The greatest sensitivity to the effect of Al or Se was exhibited by glutathione reductase. Exposure to both doses of Al or Se resulted in statistically significant increase in glutathione reductase activity in both brain and liver. It was concluded that 8-week exposure to Se caused a statistically significant increase in superoxide dismutase, catalase and glutathione reductase activities in mouse brain and/or liver, however, these changes were dependent on the used dose. The exposure to both Al doses caused a statistically significant increase only in glutathione reductase activity of both organs. Full article

The hydrogenation and hydrodeoxygenation (HDO) of dihydroxybenzene isomers, catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene) and hydroquinone (1,4-dihydroxybenzene) was studied in the liquid phase over a Rh/silica catalyst at 303–343 K and 3 barg hydrogen pressure. The following order of reactivity, resorcinol > catechol > hydroquinone (meta > ortho > para) was obtained. Kinetic analysis revealed that catechol had a negative order of reaction whereas both hydroquinone and resorcinol gave positive half-order suggesting that catechol is more strongly adsorbed. Activation energies of ~30 kJ·mol⁻¹ were determined for catechol and hydroquinone, while resorcinol gave a value of 41 kJ·mol⁻¹. Resorcinol, and similarly hydroquinone, gave higher yields of the hydrogenolysis products (cyclohexanol, cyclohexanone and cyclohexane) with a cumulative yield of ~40%. In contrast catechol favoured hydrogenation, specifically to cis-1,2-dihydroxycyclohexane. It is proposed that cis-isomers are formed from hydrogenation of dihydroxycyclohexenes and high selectivity to cis-1,2-dihydroxycyclohexane can be explained by the enhanced stability of 1,2-dihydroxycyclohex-1-ene relative to other cyclohexene intermediates of catechol, resorcinol or hydroquinone. Trans-isomers are not formed by isomerisation of the equivalent cis-dihydroxycyclohexane but by direct hydrogenation of 2/3/4-hydroxycyclohexanone. The higher selectivity to HDO for resorcinol and hydroquinone may relate to the reactive surface cyclohexenes that have a C=C double bond β-γ to a hydroxyl group aiding hydrogenolysis. Using deuterium instead of hydrogen revealed that each isomer had a unique kinetic isotope effect and that HDO to cyclohexane was dramatically affected. The delay in the production of cyclohexane suggest that deuterium acted as an inhibitor and may have blocked the specific HDO site that results in cyclohexane formation. Carbon deposition was detected by temperature programmed oxidation (TPO) and revealed three surface species. Full article

A 20 wt% Co-0.05 wt% Pt/γ-Al₂O₃ catalyst was investigated to obtain a fundamental understanding of the effect of CO partial pressure (constant H₂ partial pressure) on important kinetic parameters of the methanation reaction (x vol% CO/25 vol% H₂, x = 3, 5 and 7) by performing advanced transient isotopic and operando diffuse reflectance infrared Fourier transform spectroscopy–mass spectrometry (DRIFTS-MS) experiments. Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments conducted at 1.2 bar, 230 °C after 5 h in CO/H₂ revealed that the surface coverages, θ_CO and θ_CHx and the mean residence times, τ_CO, and τ_CHx (s) of the reversibly adsorbed CO-s and active CH_x-s (C_α) intermediates leading to CH₄, respectively, increased with increasing CO partial pressure. On the contrary, the apparent activity (k_eff, s⁻¹) of CH_x-s intermediates, turnover frequency (TOF, s⁻¹) of methanation reaction, and the CH₄-selectivity (S_CH4, %) were found to decrease. Transient isothermal hydrogenation (TIH) following the SSITKA step-gas switch provided important information regarding the reactivity and concentration of active (C_α) and inactive -C_xH_y (C_β) carbonaceous species formed after 5 h in the CO/H₂ reaction. The latter C_β species were readily hydrogenated at 230 °C in 50%H₂/Ar. The surface coverage of C_β was found to vary only slightly with increasing CO partial pressure. Temperature-programmed hydrogenation (TPH) following SSITKA and TIH revealed that other types of inactive carbonaceous species (C_γ) were formed during Fischer-Tropsch Synthesis (FTS) and hydrogenated at elevated temperatures (250–550 °C). The amount of C_γ was found to significantly increase with increasing CO partial pressure. All carbonaceous species hydrogenated during TIH and TPH revealed large differences in their kinetics of hydrogenation with respect to the CO partial pressure in the CO/H₂ reaction mixture. Operando DRIFTS-MS transient isothermal hydrogenation of adsorbed CO-s formed after 2 h in 5 vol% CO/25 vol% H₂/Ar at 200 °C coupled with kinetic modeling (H-assisted CO hydrogenation) provided information regarding the relative reactivity (k_eff) for CH₄ formation of the two kinds of linear-type adsorbed CO-s on the cobalt surface. Full article

High temperature water-gas shift (HT-WGS) is an industrially highly relevant reaction. Moreover, climate change and the resulting necessary search for sustainable energy sources are making WGS and reverse-WGS catalytic key reactions for synthetic fuel production. Hence, extensive research has been done to develop improved or novel catalysts. An extremely promising material class for novel highly active HT-WGS catalysts with superior thermal stability are perovskite-type oxides. With their large compositional flexibility, they enable new options for rational catalyst design. Particularly, both cation sites (A and B in ABO₃) can be doped with promoters or catalytically active elements. Additionally, B-site dopants are able to migrate to the surface under reducing conditions (a process called exsolution), forming catalytically active nanoparticles and creating an interface that can strongly boost catalytic performance. In this study, we varied A-site composition and B-site doping (Ni, Co), thus comparing six novel perovskites and testing them for their HT-WGS activity: La_0.9Ca_0.1FeO_3-δ, La_0.6Ca_0.4FeO_3-δ, Nd_0.9Ca_0.1FeO_3-δ, Nd_0.6Ca_0.4FeO_3-δ, Nd_0.6Ca_0.4Fe_0.9Ni_0.1O_3-δ and Nd_0.6Ca_0.4Fe_0.9Co_0.1O_3-δ. Cobalt and Nickel doping resulted in the highest activity observed in our study, highlighting that doped perovskites are promising novel HT-WGS catalysts. The effect of the compositional variations is discussed considering the kinetics of the two partial reactions of WGS-CO oxidation and water splitting. Full article

Ag–CeO₂ catalysts (20 mol % Ag) were synthesized using different techniques (co-precipitation, impregnation, and impregnation of pre-reduced ceria), characterized by XRD, N₂ sorption, TEM, H₂-TPR methods, and probed in room-temperature p-nitrophenol reduction into p-aminophenol in aqueous solution at atmospheric pressure. The catalyst preparation method was found to determine the textural characteristics, the oxidation state and distribution of silver and, hence, the catalytic activity in the p-nitrophenol reduction. The impregnation technique was the most favorable for the formation over the ceria surface of highly dispersed silver species that are active in the p-nitrophenol reduction (the first-order rate constant k = 0.656 min⁻¹). Full article

Black TiO₂ with doped nitrogen and modified carbon (b-N-TiO₂/C) were successfully prepared by sol-gel method in the presence of urea as a source of nitrogen and carbon. The photocatalysts were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, electron paramagnetic resonance (EPR), and UV-vis diffuse reflectance spectra (DRS). The doped nitrogen, introduced defects, and modified carbon played a synergistic role in enhancing photocatalytic activity of b-N-TiO₂/C for the degradation of chlorophyll-a in algae cells. The sample, with a proper amount of phase composition and oxygen vacancies, showed the highest efficiency to degrade chlorophyll-a, and the addition of H₂O₂ promoted this photocatalysis degradation. Based on the trapping experiments and electron spin resonance (ESR) signals, a photocatalytic mechanism of b-N-TiO₂/C was proposed. In the photocatalytic degradation of chlorophyll-a, the major reactive species were identified as OH and O₂⁻. This research may provide new insights into the photocatalytic inactivation of algae cells by composite photocatalysts. Full article

The hybrid materials that are created by supporting or incorporating polyoxometalates (POMs) into/onto metal–organic frameworks (MOFs) have a unique set of properties. They combine the strong acidity, oxygen-rich surface, and redox capability of POMs, while overcoming their drawbacks, such as difficult handling, a low surface area, and a high solubility. MOFs are ideal hosts because of their high surface area, long-range ordered structure, and high tunability in terms of the pore size and channels. In some cases, MOFs add an extra dimension to the functionality of hybrids. This review summarizes the recent developments in the field of POM@MOF hybrids. The most common applied synthesis strategies are discussed, together with major applications, such as their use in catalysis (organocatalysis, electrocatalysis, and photocatalysis). The more than 100 papers on this topic have been systematically summarized in a handy table, which covers almost all of the work conducted in this field up to now. Full article

Herein, a novel process of diesel exhaust purification by non-thermal plasma combined with wood fiber has been investigated to understand the effect of purification efficiency on the emission. The dielectric barrier discharge (DBD) and wood fiber (WF) improved removal efficiency of nitrogen oxide (NO_x) owing to the positive activity of oxygen-containing functional groups (such as O–H groups or C–O groups) on the wood surface, which promoted the removal of NO_x by 10%–13%. The mechanism to remove NO_x in the presence of wood fibers was also deduced through FTIR spectra. When carbon black was loaded on the wood fiber, there was simultaneous removal of carbon soot and NO_X. Although complete purification was not achieved, a high purification efficiency was obtained under the conditions of room temperature and no catalysts. These advantages highlight the importance of use of wood and non-thermal plasma (NTP), and this research work opens new avenues in the field of emissions treatment. Full article

Benzene is a typical volatile organic compound (VOC) and is found widely in industrial waste gases. In this study, trimesoyl chloride-melamine copolymer (TMP)-TiO₂ nanocomposites with excellent photocatalytic efficiency in visible-light degradation of gas-phase benzene were synthesized via an in situ hydrothermal synthesis. The optimal conditions for TMP-TiO₂ nanocomposite synthesis were determined by orthogonal experiments. The structural, physiochemical, and optoelectronic properties of the samples were studied by various analytical techniques. Ultraviolet-visible diffuse reflectance spectroscopy and surface photovoltage spectra showed that the positions of the light-absorbance edges of the TMP-TiO₂ nanocomposites were sharply red-shifted to the visible region relative to those of unmodified TiO₂. The most efficient TMP-TiO₂ nanocomposite was used for photocatalytic oxidative degradation of gas-phase benzene (initial concentration 230 mg m⁻³) under visible-light irradiation (380–800 nm); the degradation rate was 100% within 180 min. Under the same reaction conditions, the degradation rates of unmodified TiO₂ (hydrothermally synthesized TiO₂) and commercial material Degussa P25 were 19% and 23.6%, respectively. This is because the Ti–O–N and Ti–O–C bonds in TMP-modified TiO₂ reduce the band gap of TMP-TiO₂. The amide bonds in the TMP decrease the TiO₂ nanoparticle size and thus increased the specific surface area. The conjugated structures in the TMP provide abundant active sites for trapping photogenerated electrons and promote the separation and transfer of photogenerated electrons and holes. Full article

The aim of this study was to evaluate and compare the adsorption and photocatalytic activity of activated carbon-based photocatalysts. Titanium dioxide (TiO₂) and zinc oxide (ZnO) were chosen as semiconductors to prepare composites with activated carbon by the wet impregnation method. Activated carbon was prepared using as starting material onion leaves (Allium fistulosum) and as activating agent phosphoric acid (H₃PO₄). Photooxidation and batch adsorption of phenol was studied to compare the efficiency of the materials prepared. The results showed that the composite AC–TiO₂ has a greater photocatalytic activity and a better adsorption capacity compared to AC–ZnO composite. Full article

Heterogeneous photocatalysts for water decontamination were obtained by the optimized synthesis of bismuth-functionalized reduced graphene oxide (rGO/Bi) using the Hummer method and microwave treatment. Sulfamethazine (SMZ) was used as model pollutant to evaluate the photocatalytic efficacy. Photocatalysts were characterized by VP-SEM, HRTEM, XDR, XPS, RAMAN, and FTIR analyses, which confirmed the effective reduction of GO to rGO and the presence of bismuth as a crystalline phase of Bi₂O₃ polydispersed on the surface. Their performance was influenced by the rGO/Bi ratio, microwave temperature, and treatment time. The as-obtained 5%rGO/Bi composite had the highest photocatalytic activity for SMZ degradation under visible light irradiation (λ > 400 nm), achieving 100% degradation after only 2 h of treatment. The degradation yield decreased with higher percentages of rGO. Accordingly, the rGO/Bi catalysts efficiently removed SMZ, showing a high photocatalytic activity, and remained unchanged after three treatment cycles; furthermore, cytotoxicity tests demonstrated the nontoxicity of the aqueous medium after SMZ degradation. These findings support the potential value of these novel composites as photocatalysts to selectively remove pollutants in water treatment plants. Full article

The main active sites and the catalytic process in selective catalytic reduction of NO_x by CH₄ (CH₄-SCR) on In/BEA catalyst were investigated by density functional theory (DFT) using a periodic model. The [InO]⁺ and [InOH]²⁺ moieties were constructed in the channel of periodic BEA zeolite representing the Lewis and Brønsted acid sites. The electronic structures [InO]⁺ and [InOH]²⁺ were analyzed, and it was found that the [InO]⁺ group were the main active sites for CH₄ activation and NO/NO₂ adsorption in the CH₄-SCR process. CH₄ molecules could be activated on the O site of the [InO]⁺ group in In/BEA, which was resulted from the strong interactions between the C-p orbital of the CH₄ molecule and the O-p orbital of the [InO]⁺ group. CH₄ activation was the initial step in CH₄-SCR on In/BEA catalyst. NO₂ molecules were essential in the SCR process, and they could be produced by NO reacting with gaseous O₂ or the O atom of the [InO]⁺ group. The presence of NO₂ could facilitate the key intermediate nitromethane (CH₃NO₂) formation and lower the reaction barrier in the SCR process. Full article

The Pd-mediated cross-coupling of (hetero)arenes with alkenes may be an effective method for the formation of a C–C bond from two C–H bonds. Discovered by Fujiwara and co-workers in 1967, this reaction led to a number of reports that we firstly highlighted in 2011 (review with references till June 2010) and for which, we retained the name “dehydrogenative Heck reaction”. The topic, especially the reactions of five-membered heteroarenes, has been the subject of intensive research over the last ten years. The present review is limited to these dehydrogenative Heck reactions published since 2010, underlining the progress of the procedures. Full article

Photocatalytic membrane reactors (PMR), with immobilized photocatalysts, play an important role in process intensification strategies; this approach offers a simple solution to the typical catalyst recovery problem of photocatalytic processes and, by simultaneous filtration and photocatalysis of the aqueous streams, facilitates clean water production in a single unit. The synthesis of polymer photocatalytic membranes has been widely explored, while studies focused on ceramic photocatalytic membranes represent a minority. However, previous reports have identified that the successful synthesis of polymeric photocatalytic membranes still faces certain challenges that demand further research, e.g., (i) reduced photocatalytic activity, (ii) photocatalyst stability, and (iii) membrane aging, to achieve technological competitiveness with respect to suspended photocatalytic systems. The novelty of this review is to go a step further to preceding literature by first, critically analyzing the factors behind these major limitations and second, establishing useful guidelines. This information will help researchers in the field in the selection of the membrane materials and synthesis methodology for a better performance of polymeric photocatalytic membranes with targeted functionality; special attention is focused on factors affecting membrane aging and photocatalyst stability. Full article

The main objective of this study was to evaluate the effect of functionalized silica nanoparticles with Fe₂O₃, NiO, and MoO₃ metal oxides on the decomposition of asphaltenes, through an experimental simplex–centroid mixture design for surface area, asphaltene adsorption, and activation energy. The experimental nanoparticle surface area was measured by adsorption of N₂. Adsorption isotherms, and the subsequent oxidation process of asphaltenes, were performed through batch adsorption experiments and thermogravimetric analysis, respectively. Among the monometallic systems, the presence of iron increased the affinity between the nanoparticle and the asphaltenes, and a higher metal oxide load increased the adsorptive capacity of the system. For the pairings evaluated, there was better synergy between iron and nickel, with the participation of the former being slightly superior. In the mixture design that included three transition elements, the participation of molybdenum was not significant, and the adsorption of asphaltenes was dominated by the active sites formed by the other two transition element oxides. The mixture design created to minimize the activation energy showed that the interaction of the three transition elements is important and can be evidenced in the interaction coefficients. Full article

Styrene and indole monooxygenases (SMO and IMO) are two-component flavoprotein monooxygenases composed of a nicotinamide adenine dinucleotide (NADH)-dependent flavin adenine dinucleotide (FAD)-reductase (StyB or IndB) and a monooxygenase (StyA or IndA). The latter uses reduced FAD to activate oxygen and to oxygenate the substrate while releasing water. We circumvented the need for the reductase by direct FAD reduction in solution using the NAD(P)H-mimic 1-benzyl-1,4-dihydronicotinamide (BNAH) to fuel monooxygenases without NADH requirement. Herein, we report on the hitherto unknown solvent tolerance for the indole monooxygenase from Gemmobacter nectariphilus DSM15620 (GnIndA) and the styrene monooxygenase from Gordonia rubripertincta CWB2 (GrStyA). These enzymes were shown to convert bulky and rather hydrophobic styrene derivatives in the presence of organic cosolvents. Subsequently, BNAH-driven biotransformation was furthermore optimized with regard to the applied cosolvent and its concentration as well as FAD and BNAH concentration. We herein demonstrate that GnIndA and GrStyA enable selective epoxidations of allylic double bonds (up to 217 mU mg⁻¹) in the presence of organic solvents such as tetrahydrofuran, acetonitrile, or several alcohols. Notably, GnIndA was found to resist methanol concentrations up to 25 vol.%. Furthermore, a diverse substrate preference was determined for both enzymes, making their distinct use very interesting. In general, our results seem representative for many IMOs as was corroborated by in silico mutagenetic studies. Full article

Ongoing industrialization has deteriorated the global environment. Global warming is a human-induced issue affecting the environment. The alarming increase in CO₂ emissions is among the major contributors to global warming. The conversion of CO₂ to methanol is an economically viable and environmentally friendly solution to mitigate its concentration. Here, hydrogenation of CO₂ was studied over carbon nanofiber-based Cu/ZrO₂ catalysts. Kinetics investigations were carried out for the reaction. Overall, kinetics data indicated that CO₂ conversion follows a pseudo-first-order reaction. The kinetics studies were further modeled by using an artificial neural network, which supported the experimental kinetics study. Full article

Manganese and iron oxides catalysts supported on silicalite-1 and titanium silicalite-1 (TS-1) are synthesized by the wet impregnation method for the selective catalytic reduction (SCR) of NO_x with NH₃ (NH₃-SCR), respectively. The optimized catalyst demonstrates an increased NO_x conversion efficiency of 20% below 150 °C, with a space velocity of 18,000 h⁻¹, which can be attributed to the incorporation of Ti species. The presence of Ti species enhances surface acidity and redox ability of the catalyst without changing the structure of supporter. Moreover, further researches based on in situ NH₃ adsorption reveal that Lewis acid sites linked to Mn⁴⁺ on the surface have a huge influence on the improvement of denitration efficiency of the catalyst at low temperatures. Full article

DHA/EPA ethyl ester is mainly used in the treatment of arteriosclerosis and hyperlipidemia. In this study, DHA+EPA ethyl ester was synthesized via lipase-catalyzed acidolysis of ethyl acetate (EA) with DHA+EPA concentrate in n-hexane using Novozym^® 435. The DHA+EPA concentrate (in free fatty acid form), contained 54.4% DHA and 16.8% EPA, was used as raw material. A central composite design combined with response surface methodology (RSM) was used to evaluate the relationship between substrate concentrations and initial rate of DHA+EPA ethyl ester production. The results indicated that the reaction followed the ordered mechanism and as such, the ordered mechanism model was used to estimate the maximum reaction rate (Vmax) and kinetic constants. The ordered mechanism model was also combined with the batch reaction equation to simulate and predict the conversion of DHA+EPA ethyl ester in lipase-catalyzed acidolysis. The integral equation showed a good predictive relationship between the simulated and experimental results. 88–94% conversion yields were obtained from 100–400 mM DHA+EPA concentrate at a constant enzyme activity of 200 U, substrate ratio of 1:1 (DHA+EPA: EA), and reaction time of 300 min. Full article

This work focuses on the development of a Pt/Re/CeO₂-based structured catalyst for a single stage water–gas shift process. In the first part of the work, the activity in water–gas shift reactions was evaluated for three Pt/Re/CeO₂-based powder catalysts, with Pt/Re ratio equal to 1/1, 1/2 ad 2/1 and total loading ≈ 1 wt%. The catalysts were prepared by sequential dry impregnation of commercial ceria, with the salts precursors of rhenium and platinum; the activity tests were carried out by feeding a reacting mixture with a variable CO/H₂O ratio, equal to 7/14, 7/20 and 7/24, and the kinetic parameters were determined. The model which better described the experimental results involves the water–gas shift (WGS) reaction and CO as well as CO₂ methanation. The preliminary tests showed that the catalyst with the Pt/Re ratio equal to 2/1 had the best performance, and this was selected for further investigations. In the second part of the work, a structured catalyst, obtained by coating a commercial aluminum alloy foam with the chosen catalytic formulation, was prepared and tested in different reaction conditions. The results demonstrated that a single stage water–gas shift process is achievable, obtaining a hydrogen production rate of 18.7 mmol/min at 685 K, at τ = 53 ms, by feeding a simulated reformate gas mixture (37.61 vol% H₂, 9.31 vol% CO₂, 9.31 vol% CO, 42.19 vol% H₂O, 1.37 vol% CH₄). Full article