Catalysts

In this paper, a novel [email protected] nanosphere (TiO₂@CoAl-LDH) based on layered double hydroxide (LDH) combined with a nano-TiO₂ semiconductor was synthesized and introduced to cementitious materials via spraying technology and a smearing method. The compatibility with a cementitious matrix and the effects of TiO₂@CoAl-LDH on cement hydration, surface microstructure, and the microscopic mechanical properties of mortar were investigated by AFM, microhardness testing, FESEM, and BET analysis. Meanwhile, the effects of TiO₂@CoAl-LDH introduction methods on the photocatalytic performance and durability of the photocatalyst were systematically evaluated by methylene blue (MB) removal ratio and wear testing. The results show that TiO₂@CoAl-LDH exhibits enhanced compatibility with cementitious matrices and a higher photocatalytic capacity than individual CoAl-LDH and nano-TiO₂. The photocatalytic mortar prepared via spraying technology (CM-C) displays a higher photocatalytic capacity than that prepared via the smearing method (CM-S). Among them, the mortar with two layers of photocatalytic coatings (CM-C2) has the highest MB removal ratio, which reached 95.1% within 120 min of UV-visible light irradiation. While on the other hand, the wear test revealed that the smeared mortar has a higher photocatalytic capacity and better photocatalyst durability than the sprayed mortar. This work is expected to contribute to the development of multifunctional sustainable building materials. Full article

The present study aims to develop new energetic composites containing nanostructured nitrocellulose (NNC) or nitrated cellulose (NC), hydrazinium nitro triazolone (HNTO), and MgAl-CuO nanothermite. The prepared energetic formulations (NC/HNTO/MgAl-CuO and NNC/HNTO/MgAl-CuO) were analyzed using various analytical techniques, such as Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), thermogravimetry (TGA), and differential scanning calorimetry (DSC). The outstanding catalytic impact of MgAl-CuO on the thermal behavior of the developed energetic composites was elucidated by kinetic modeling, applied to the DSC data using isoconversional kinetic methods, for which a considerable drop in the activation energy was acquired for the prepared formulations, highlighting the catalytic influence of the introduced MgAl-CuO nanothermite. Overall, the obtained findings demonstrated that the newly elaborated NC/HNTO/MgAl-CuO and NNC/HNTO/MgAl-CuO composites could serve as promising candidates for application in the next generation of composite explosives and high-performance propellants. Full article

In this review, we analyzed the history and the past and present trends in photocatalysis research, trying to outline possible scenarios for the future in the medium term. The in-depth analysis of the literature reported here—from a mere bibliometric point of view—allowed us to divide the history of photocatalysis into four different periods characterized by different maturity of the topic and different bibliometric features. The turn of the 20th century saw an explosion in scientific production, which is still continuing now and has reached more than 15,000 papers published each year. Research interest is still growing significantly, and the analysis of different keywords suggests that such growth is substantial and not merely due to “publish or perish” behavior. The analysis of the most-investigated topics in the field of photocatalysis highlighted that, during its history, the focus of the research moved from inorganic oxides to carbon and hybrid materials. Concomitantly, the investigation of the “geography” of photocatalysis allowed us to underline its evolution over the years, with the repositioning of its center of mass from the Atlantic Ocean (USA and Europe) to Asia (China and India). Photocatalysis is active as never before but still awaiting major breakthroughs, which would allow a much broader technological and commercial output. Without such breakthroughs in this decade, the growth in scientific interest could level out or even decrease. Full article

Nanoparticles of TiO₂ are suitable for many catalytic and photocatalytic applications due to their extraordinary properties such as superhydrophobicity, semiconductivity, electron-rich, and environmental compatibility. The main crystalline phases of TiO₂, anatase, and rutile possess different crystal structures, crystallinity, crystalline sizes, and specific surface areas, and these characteristics directly affect the catalytic performance of TiO₂. In the present study, domestic carbon material enhanced with TiO₂ nanoparticles was synthesized and used for the construction of a modified carbon paste electrode. The electrocatalytic activity of the modified electrodes was investigated depending on the TiO₂ crystalline phases in the electrode material. Furthermore, the obtained working electrode was utilized for triclosan detection. Under optimized experimental conditions, the developed electrode showed a submicromolar triclosan detection limit of 0.07 µM and a wide linear range of 0.1 to 15 µM. The relative standard deviations for repeatability and reproducibility were lower than 4.1%, and with satisfactory selectivity, the proposed system was successfully applied to triclosan monitoring in groundwater. All these results confirm that the sustainable production of new and domestically prepared materials is of great benefit in the field of electrocatalysis and that the morphology of such produced materials is strongly related to their catalytic properties. Full article

Enzymes have several excellent catalytic features, and the last few years have seen a revolution in biocatalysis, which has grown from using one enzyme to using multiple enzymes in cascade reactions, where the product of one enzyme reaction is the substrate for the subsequent one. However, enzyme stability remains an issue despite the many benefits of using enzymes in a catalytic system. When enzymes are exposed to harsh process conditions, deactivation occurs, which changes the activity of the enzyme, leading to an increase in reaction time to achieve a given conversion. Immobilization is a well-known strategy to improve many enzyme properties, if the immobilization is properly designed and controlled. Enzyme co-immobilization is a further step in the complexity of preparing a biocatalyst, whereby two or more enzymes are immobilized on the same particle or support. One crucial problem when designing and using co-immobilized enzymes is the possibility of using enzymes with very different stabilities. This paper discusses different scenarios using two co-immobilized enzymes of the same or differing stability. The effect on operational performance is shown via simple simulations using Michaelis–Menten equations to describe kinetics integrated with a deactivation term. Finally, some strategies for overcoming some of these problems are discussed. Full article

The cobalt(II) chloride N,N,N-pincer complexes, [2-{(2,4-(C₁₅H₁₃)₂-6-FC₆H₂)N=CMe}-6-(ArN=CMe)C₅H₃N]CoCl₂ (Ar = 2,6-Me₂C₆H₃) (Co1), 2,6-Et₂C₆H₃ (Co2), 2,6-i-Pr₂C₆H₃ (Co3), 2,4,6-Me₃C₆H₂ (Co4), 2,6-Et₂-4-MeC₆H₂ (Co5), and [2,6-{(2,4-(C₁₅H₁₃)₂-6-FC₆H₂)N=CMe}₂C₅H₃N]CoCl₂ (Co6), each containing at least one N-2,4-bis(dibenzosuberyl)-6-fluorophenyl group, were synthesized in good yield from their corresponding unsymmetrical (L1–L5) and symmetrical bis(imino)pyridines (L6). The molecular structures of Co1 and Co2 spotlighted their distorted square pyramidal geometries (τ₅ value range: 0.23–0.29) and variations in steric hindrance offered by the dissimilar N-aryl groups. On activation with either MAO or MMAO, Co1–Co6 all displayed high activities for ethylene polymerization, with levels falling in the order: Co1 > Co4 > Co5 > Co2 > Co3 > Co6. Indeed, the least sterically hindered 2,6-dimethyl Co1 in combination with MAO exhibited a very high activity of 1.15 × 10⁷ g PE mol⁻¹ (Co) h⁻¹ at the operating temperature of 70 °C, which dropped by only 15% at 80 °C and 43% at 90 °C. Vinyl-terminated polyethylenes of high linearity and narrow dispersity were generated by all catalysts, with the most sterically hindered, Co3 and Co6, producing the highest molecular weight polymers [M_w range: 30.26–33.90 kg mol⁻¹ (Co3) and 42.90–43.92 kg mol⁻¹ (Co6)]. In comparison with structurally related cobalt catalysts, it was evident that the presence of the N-2,4-bis(dibenzosuberyl)-6-fluorophenyl groups had a limited effect on catalytic activity but a marked effect on thermal stability. Full article

Ternary metal oxides (TMOs) with flexible band structures are of significant potential in the field of photocatalysis. The efficient utilization of renewable and green solar energy is of great importance to developing photocatalysts. To date, a wide range of TMOs systems has been developed as photocatalysts for water and air purification, but their practical applications in visible light-assisted chemical reactions are hindered mainly by its poor visible light absorption capacity. Introduction of N atoms into TMOs can narrow the band-gap energy to a lower value, enhance the absorption of visible light and suppress the recombination rate of photogenerated electrons and holes, thus improving the photocatalytic performance. This review summarizes the recent research on N-modified TMOs, including the influence of N doping amounts, N doping sites, and N-induced phase transformation. The introduced N greatly tuned the optical properties, electronic structure, and photocatalytic activity of the TMOs. The optimal N concentration and the influence of N doping sites are investigated. The substitutional N and interstitial N contributed differently to the band gap and electron transport. The introduced N can tune the vacancies in TMOs due to the charge compensation, which is vital for inducing different activity and selectivity. The topochemical ammonolysis process can convert TMOs to oxynitride with visible light absorption. By altering the band structures, these oxynitride materials showed enhanced photocatalytic activity. This review provides an overview of recent advances in N-doped TMOs and oxynitrides derived from TMOs as photocatalysts for environmental applications, as well as some relevant pointers for future burgeoning research development. Full article

5−hydroxymethylfurfural (HMF), as one of the top ten important platform chemicals, can be used to produce 2,5−furandicarboxylic acid (FDCA), 2,5−dimethyl furan (DMF), levulinic acid, and other chemicals. An environmentally friendly system for the synthesis of sulfonated carbon materials from discarded masks has been proposed. A series of mask−based solid acid catalysts (bMC−SO₃H) were prepared by a simple two−step process. Mechanochemical pretreatment (ball milling) of waste mask and sulfonated group precursor, followed by thermal carbonization under nitrogen gas, were used to synthesize sulfonated porous carbon. The total acid amount of the prepared bMC−SO₃H was measured by the Boehm method, which exhibited 1.2–5.3 mmol/g. The addition of the sulfonated group precursor in the mechanochemical treatment (ball milling) process caused intense structure fragmentation of the discarded masks. These sulfonated porous carbons (bMC(600)−SO₃H) as solid acid catalysts achieved fructose conversion of 100% and HMF yield of 82.1% after 120 min at 95 °C in 1−butyl−3−methylimidazolium chloride. The bMC−SO₃H could be reused five times, during which both the HMF yield and fructose conversion were stable. This work provides a strategy for the synthesis of sulfonated carbon from discarded masks and efficient catalyzed fructose upgrading to HMF. Full article

The lipase kinetic resolution (KR) of aryloxy-propan-2-yl acetates, via hydrolysis, produced enantiomerically pure/enantioenriched mexiletine intermediates and analogs. Racemic acetates rac-1-(2,6-dimethylphenoxy)propan-2-yl acetate (rac-5a), rac-1-(2,4-dimethylphenoxy)propan-2-yl acetate (rac-5b), rac-1-(o-tolyloxy)propan-2-yl acetate (rac-5c) and rac-1-(naphthalen-1-yloxy)propan-2-yl acetate (rac-5d) were used as substrates. A preliminary screening (24 h, phosphate buffer pH 7.0 with 20% acetonitrile as co-solvent, 30 °C and enzyme: substrate ratio of 2:1, m:m) was carried out with twelve lipases using acetate 5a as substrate. Two enzymes stood out in the KR of 5a, the Amano AK lipase from Pseudomonas fluorescens and lipase from Thermomyces lanuginosus (TLL) immobilized on Immobead 150. Under these conditions, both the (R)-1-(2,6-dimethylphenoxy)propan-2-ol [(R)-4a] and the remaining (S)-1-(2,6-dimethylphenoxy)propan-2-yl acetate [(S)-5a] were obtained with enantiomeric excess (ee) > 99%, 50% conversion and enantiomeric ratio (E) > 200. The KR study was expanded to racemic acetates 5b-d, leading to the corresponding chiral remaining acetates with ≥ 95% ee, and the alcohols 4b-d with ≥ 98% ee, and conversion values close to 50%. The best conditions for KRs of rac-5b-d involved the use of lipase from P. fluorescens or TLL immobilized on Immobead 150, 24 or 48 h and 30 °C. These intermediates had their absolute configurations determined using ¹H NMR spectroscopy (Mosher’s method), showing that the KRs of these acetates obeyed the Kazlauskas’ rule. Molecular docking studies corroborated the experimental results, indicating a preference for the hydrolysis of (R)-5a-d. Full article

Phenol and its derivatives are present in effluents from several industrial processes, such as petroleum refining (produced water) and the pharmaceutical industry, and they are highly toxic. The present work elaborated a new catalyst for the removal of phenol and its derivatives. The photocatalyst was prepared by a simple method from the ammonium oxalate of niobium and nickel nitrate, resulting in heterostructures (principally NaNbO₃/NaNb₃O₈ and a lesser amount of NiO) named NiNb. Platinum was deposited on this catalyst (NiNb/Pt catalyst), and its photocatalytic activity was tested on the degradation of phenol in seawater and distilled water, in the presence and absence of UV-C light (germicidal, λ = 254 nm), and with varying concentrations of platinum and varying pH of the solution. The catalyst was characterized by different techniques (SEM, EDS, DRS, XRD, TXRF, S_BET,). The results of the study showed that the NiNb/Pt catalyst achieved 65% phenol removal in seawater and about 57% removal in distilled water. The reuse of the catalyst was also studied, and the photocatalytic mechanism was investigated by tests with scavenger agents and terephthalic acid. Full article

Fluorinated Fe₃O₄ microspheres with 7.1 ± 1.4 wt% of fluoride (F-Fe₃O₄-1) were prepared via glycothermal synthesis. Fluorination significantly enhanced the activity of F-Fe₃O₄-1 in catalytic wet peroxide oxidation of anionic dyes (including orange G (OG) and congo red) at pH ~7. However, the promotional effect of fluorination became less obvious for amphoteric rhodamine B and was not observed for cationic methylene blue. After reacting with H₂O₂ (40 mM) for 2 h at pH 6.5 and 40 °C, the decolorization rates of OG (0.1 mM) and the pseudo-first-order rate constant were 96.8% and 0.0284 min⁻¹ over F-Fe₃O₄-1 versus 17.6% and 0.0011 min⁻¹ over unmodified Fe₃O₄. The effects of reaction parameters (initial H₂O₂ concentration and pH value and reaction temperature) on OG decolorization with H₂O₂ over F-Fe₃O₄-1 were investigated. The reusability of F-Fe₃O₄-1 was demonstrated by OG decolorization in eight consecutive runs. Fluorination increased the isoelectric point of F-Fe₃O₄-1 to 8.7 and facilitated the adsorption and degradation of anionic dyes on the surface of F-Fe₃O₄-1 at pH ~7. Scavenging tests and EPR spectra supported that hydroxyl radicals were the main reactive species for the OG decolorization over F-Fe₃O₄-1. Full article

Perovskite samples of the LaMn_1−xFe_xO₃ (x = 0–1) series were prepared by the Pechini method; their physicochemical properties were studied using XRD, HRTEM, XPS, and BET, and their catalytic activity was estimated in nitrous oxide decomposition and methane and CO oxidation reactions. In methane and CO oxidation reactions, all intermediate (0 < x < 1) samples of the series exhibited a lower catalytic activity normalized to the unit surface area as compared to the extreme terms, whereas in the nitrous oxide decomposition all intermediate samples were more active than extreme terms of the series. Different dependences of activities on the composition obtained in the study for the tested reactions involving the catalyst oxygen are caused by differences in the reaction mechanisms. Full article

The development and commercialization of direct ethanol fuel cells requires active and durable electro-catalysts towards the ethanol oxidation reactions (EOR). Rational composition and morphology control of Pt-based alloy nanocrystals can not only enhance their EOR reactivity but also reduce the consumption of precious Pt. Herein, PtCu nanocubes (NCs)/CB enclosed by well-defined (100) facets were prepared by solution synthesis, exhibiting much higher mass activity (4.96 A mg_Pt⁻¹) than PtCu nanoparticles (NPs)/CB with irregular shapes (3.26 A mg_Pt⁻¹) and commercial Pt/C (1.67 A mg_Pt⁻¹). CO stripping and in situ Fourier transform infrared spectroscopy (FTIR) experiments indicate that the alloying of Cu enhanced the adsorption of ethanol, accelerated the subsequent oxidation of intermediate species, and increased the resistance to CO poisoning of PtCu NCs/CB, as compared with commercial Pt/C. Therefore, alloying Pt with earth-abundant Cu under rational composition and surface control can optimize its surface and electronic structures and represents a promising strategy to promote the performance of electro-catalysts while reduce the use of precious metals. Full article

Ammonia (NH₃) plays an irreplaceable role in human life as a promising energy carrier and indispensable chemical raw material. Nitrate electroreduction to ammonium (NRA) not only removes nitrate pollutants, but also can be used for efficient NH₃ production under ambient conditions. However, achieving high efficiency and selectivity of electrocatalysts is still a great challenge. Herein, a complex Cu₂(NO₃)₄(BMMB)·H₂O with a bicopper core is assembled by Cu(NO₃)₂·3H₂O and 1,4-bis{[2-(2’-pyridyl)benzimidazolyl]methyl}benzene (BMMB) for NRA under alkaline conditions. The optimal sample showed excellent nitrate reduction performance with the NO₃⁻ conversion rate of 70%, Faradaic efficiency of up to 90%, and NH₃ selectivity of more than 95%. The high-catalytic activity is mainly due to the ingeniously designed copper cores with strong affinity for NO₃⁻, which accelerates the transferring rate of adsorbed nitrate on the Cu surface and increases the efficiency of rate-determining step (NO₃⁻ → NO₂⁻) in the whole catalytic process. Therefore, the transformation of surface-exposed nitrate can be rapidly catalyzed by the Cu active sites, facilitating the conversion efficiency of nitrate. Full article

Hydrazine oxidation in single-atom catalysts (SACs) could exploit the efficiency of metal atom utilization, which is a substitution for noble metal-based electrolysers that results in reduced overall cost. A well-established ruthenium single atom over mesoporous carbon nitride (SRu-mC₃N₄) catalyst is explored for the electro-oxidation of hydrazine as one of the model reactions for direct fuel cell reactions. The electrochemical activity observed with linear sweep voltammetry (LSV) confirmed that SRu-mC₃N₄ shows an ultra-low onset potential of 0.88 V vs. RHE, and with a current density of 10 mA/cm² the observed potential was 1.19 V vs. RHE, compared with mesoporous carbon nitride (mC₃N₄) (1.77 V vs. RHE). Electrochemical impedance spectroscopy (EIS) and chronoamperometry (i-t) studies on SRu-mC₃N₄ show a smaller charge-transfer resistance (R_Ct) of 2950 Ω and long-term potential, as well as current stability of 50 h and 20 mA/cm², respectively. Herein, an efficient and enhanced activity toward HzOR was demonstrated on SRu-mC₃N₄ from its synergistic platform over highly porous C₃N₄, possessing large and independent active sites, and improving the subsequent large-scale reaction. Full article

NiMo sulfide catalysts were prepared by the impregnation of high surface area supports with an aqueous solution made of NiCO₃·2Ni(OH)₂, MoO₃ and citric acid, followed by freeze drying and sulfidation in H₂S/H₂ mixture. N₂ physisorption and X-ray diffraction were selected to investigate the amphoteric oxides Al₂O₃ and TiO₂, acidic SiO₂-Al₂O₃ and activated carbon supports, fresh prepared sulfide NiMo catalysts and spent catalysts after model parallel reaction of octanoic acid deoxygenation and 1-benzothiophene hydrodesulfurization. The studied mesoporous amphoteric oxides Al₂O₃ and TiO₂ did not lead to highly active NiMo catalysts due to the low hydrothermal stability of these supports during the preparation of the active sulfide phase and deoxygenation reaction. The most active catalyst based on oxidic support was the NiMo sulfide supported on acidic mesoporous SiO₂-Al₂O₃, which was explained by the increased stability of this support to the water and CO/CO₂ mixture during the activation of the sulfidic phase and deoxygenation reaction. The extraordinarily high stability of the activated carbon support led to outstanding activities of the sulfidic NiMo/C catalyst. Full article

The present communication describes the results of the performance and the assessment of a sensor based on a solid oxide electrolyte with a composition of 0.9ZrO₂ + 0.1Y₂O₃ (YSZ), equipped with a ceramic diffusion barrier for measuring the water vapor and hydrogen content in air. The possibility of determining the concentration of water vapor and hydrogen in the air is based on the measurement of the limiting current value. For the calculation of the steam and hydrogen concentration in ambient air, analytical expressions were obtained and applied, using the limiting current values measured in air with a standard oxygen concentration of 20.9 vol.% and in the analyzed air. A two-stage method for the determination of the hydrogen and steam amount in ambient air is proposed. It is stated that the sensor operates successfully at the temperature of 700 °C and can be applied for the continuous determination of steam or hydrogen concentrations in air. Full article

Photocatalytic water oxidation over titanium dioxide (TiO₂) was overviewed by surveying briefly the history of water photo-oxidation, followed by profiling the research for the molecular mechanism of oxygen evolution reaction (OER) at the TiO₂ surface. As the experimental approach to investigate the reaction mechanism, ESR, NMR, and STM were described as well as FTIR spectroscopy. Detection of reactive oxygen species, which are the intermediate species in the OER, was also involved in discussing the mechanism. As the theoretical approach to the reaction mechanism, some research with density functional theory (DFT) for anatase (101) surface was illustrated. Since the OER activity of rutile TiO₂ is higher than that of anatase, and the rutile (011) surface has been assigned to the oxidation facet, we performed a DFT calculation for a (011) surface model molecule. The results were successfully discussed with the reported mechanism. The first oxidation step occurs at the bridging OH site, which faces a Ti_5C site. The water molecule which coordinates both sites is oxidized, and the resultant radical coordinates the Ti_5C site to form a trapped hole Ti-O•. In the second step, a coordinated water molecule is oxidized at the Ti-O• site to form a Ti-OOH structure. Full article

The stability of platinized n-butylamine-intercalated layered titanate H₂La₂Ti₃O₁₀ during the process of photocatalytic hydrogen production from aqueous methanol under UV irradiation has been thoroughly investigated by means of XRD, CHN, TG, ¹³C NMR, BET, SEM and GC-MS analysis. It was revealed that n‑butylamine completely abandons the interlayer space and transforms into n‑butyraldehyde within 3 h of the reaction, while the particle morphology and specific surface area of the photocatalyst are preserved. The resulting solid phase contains carbon in at least two different oxidation states, which are attributed to the intermediate products of methanol oxidation bound to the perovskite matrix. The activity of the photocatalyst formed in this way is stable in time and strongly depends on the medium pH, which is not typical of either the parent H₂La₂Ti₃O₁₀ or TiO₂. An approximate linear equation φ ≈ 29−2∙pH holds for the apparent quantum efficiency of hydrogen production in the 220–340 nm range at 1 mol. % methanol concentration. In the acidic medium, the photocatalyst under study outperforms the platinized H₂La₂Ti₃O₁₀ by more than one order of magnitude. The variation in methanol concentration allowed a maximum quantum efficiency of hydrogen production of 44% at 10 mol. % to be reached. Full article