Sacrificial carbonaceous coating over alumina supported Ni–MoS2 catalyst for hydrodesulfurization

Recent results have evidenced that carbon plays an important role in stabilizing the structure of the active phase in catalysts. In this work, carbon-coated alumina was prepared by applying polydopamine (PDA) as a sacrificial carbon source to modify the surface properties of γ-alumina, which then was used as a support to prepare supported NiMo catalysts for hydrodesulfurization (HDS) of dibenzothiophene (DBT). NiMo/Al₂O₃ catalysts exhibited limited hydrodesulfurization performances due to their strong metal-support interaction. Herein, we report an unexpected phenomenon that sacrificial carbon layers can be constructed on the surface of the Al₂O₃ support from the carbonization of polydopamine (PDA) and mediated the interaction between the active site and support. Through the removal of carbon layers and sulfidation, the resulting NiMo catalysts exhibit excellent performance for HDS reaction of dibenzothiophene (DBT), which is associated with adequate loading of residual carbon species, leading to an enhanced amount of active species under sulfidation conditions. Moreover, the facile synthetic strategy can be extended to the stabilization of the active phase on a broad range of supports, providing a general approach for improving the metal-support interaction supported nanocatalysts.

Sacrificial carbon coating over NiMo/Al₂O₃ catalyst effectively tailor the interaction between the active phase and support, which result in more easily reducible active components and enhanced HDS performance.     

Enhanced degradation of dimethyl phthalate in wastewater via heterogeneous catalytic ozonation process: performances and mechanisms

Ozonation process is a promising yet challenging method for the removal of refractory organic matter due to the sluggish reaction for generating hydroxyl radical (˙OH) at a neutral pH condition. Herein, an efficient heterogeneous catalytic ozonation system using CeO₂/Al₂O₃ catalyst was developed to remove dimethyl phthalate (DMP) from wastewater. Under a neutral condition of pH = 6, this system achieved almost 100% DMP removal within 15 min at an optimized catalyst dosage of 30 g L⁻¹ and the ozone flow rate of 22.5 mg min⁻¹. Moreover, the catalytic ozonation system exhibited a stable degradation performance of DMP in a wider pH range (pH = 5–10). The results of electron paramagnetic resonance (EPR) and quantitative tests confirmed the ultrafast conversion of O₃ to ˙OH (0.774 μM min⁻¹) on the surface of CeO₂ based ceramic catalyst. The quenching experiments further supported the predominant role of ˙OH in the mineralization of DMP. These results highlight the potential of using the heterogeneous catalytic ozonation system for the efficient removal of refractory organic matter from wastewater.

An efficient heterogeneous catalytic ozonation system using CeO₂/Al₂O₃ catalyst was developed to remove dimethyl phthalate (DMP) from wastewater.     

Operando sulfur speciation during sulfur poisoning-regeneration of Ru/SiO2 and Ru/Al2O3 using non-resonant sulfur Kα1,2 emission

A periodic oxidative regeneration of a sulfur-poisoned methanation catalyst is an alternative to the expensive state-of-the-art process of syngas cleaning using wet scrubbers. Here we have employed operando X-ray emission spectroscopy (XES) to study sulfur speciation on Ru/SiO₂ and Ru/Al₂O₃ during methanation in the presence of H₂S and subsequent regeneration in dilute O₂ at 360 °C. XES allowed us to obtain semi-quantitative sulfur speciation and to monitor changes in the absolute sulfur concentration. It was established that Al₂O₃, in contrast to SiO₂, forms sulfite/sulfate species by reacting with SO₂, which is released from the poisoned Ru surface upon oxidative treatment. The concentration of sulfite/sulfate species is reduced upon switching the feed to H₂/CO while no simultaneous increase in sulfide concentration is observed. For both catalysts, the regenerative treatment removes adsorbed sulfur as SO₂ only partially, which we propose is the main reason for the incomplete activity recovery of the poisoned catalyst after regeneration.

Operando S Kα X-ray emission spectroscopy allows for a quantitative understanding of the sulfur poisoning and regeneration mechanism of state-of-the-art methanation catalysts used for the wood to synthetic natural gas process.     

Continuous selective deoxygenation of palm oil for renewable diesel production over Ni catalysts supported on Al2O3 and La2O3–Al2O3

The present study provides, for the first time in the literature, a comparative assessment of the catalytic performance of Ni catalysts supported on γ-Al₂O₃ and γ-Al₂O₃ modified with La₂O₃, in a continuous flow trickle bed reactor, for the selective deoxygenation of palm oil. The catalysts were prepared via the wet impregnation method and were characterized, after calcination and/or reduction, by N₂ adsorption/desorption, XRD, NH₃-TPD, CO₂-TPD, H₂-TPR, H₂-TPD, XPS and TEM, and after the time-on-stream tests, by TGA, TPO, Raman and TEM. Catalytic experiments were performed between 300–400 °C, at a constant pressure (30 bar) and different LHSV (1.2–3.6 h⁻¹). The results show that the incorporation of La₂O₃ in the Al₂O₃ support increased the Ni surface atomic concentration (XPS), affected the nature and abundance of surface basicity (CO₂-TPD), and despite leading to a drop in surface acidity (NH₃-TPD), the Ni/LaAl catalyst presented a larger population of medium-strength acid sites. These characteristics helped promote the SDO process and prevented extended cracking and the formation of coke. Thus, higher triglyceride conversions and n-C₁₅ to n-C₁₈ hydrocarbon yields were achieved with the Ni/LaAl at lower reaction temperatures. Moreover, the Ni/LaAl catalyst was considerably more stable during 20 h of time-on-stream. Examination of the spent catalysts revealed that both carbon deposition and degree of graphitization of the surface coke, as well as, the extent of sintering were lower on the Ni/LaAl catalyst, explaining its excellent performance during time-on-stream.

Highly selective and stable Ni supported on La₂O₃–Al₂O₃ catalyst on the deCO/deCO₂ reaction paths for the production of renewable diesel.     

Oxidative desulfurization of dibenzothiophene catalyzed by α-MnO2 nanosheets on palygorskite using hydrogen peroxide as oxidant

Palygorskite (Pal)-supported α-MnO₂ nanosheets (Ns-MnPal) combine the adsorption features of Pal with the catalytic properties of α-MnO₂ nanosheets. They were prepared and examined in the catalytic oxidative desulfurization (ODS) of dibenzothiophene (DBT) from a model oil employing 30 wt% H₂O₂ as the oxidant under mild conditions. The supported catalyst was fabricated by the solvothermal method, and effective immobilization of α-MnO₂ nanosheets was confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption. The influence of various solvents, solvent volume, reaction temperature, reaction time, catalyst amount and H₂O₂/sulfur molar ratio on ODS was investigated. Using 20 mL of acetonitrile as a solvent, maximum sulfur removal of 97.7% was achieved for ODS of DBT in 1.5 h using a Ns-MnPal/oil ratio of 0.2 g L⁻¹, reaction temperature of 50 °C and H₂O₂/sulfur molar ratio of 4. As solid catalysts, supported α-MnO₂ nanosheets could be separated from the reaction readily. The catalyst was recycled seven times and showed no significant loss in activity.

Palygorskite (Pal)-supported α-MnO₂ nanosheets (Ns-MnPal) combine the adsorption features of Pal with the catalytic properties of α-MnO₂ nanosheets.     

A study on the viscosity reduction mechanism of high-filled silicone potting adhesive by the formation of Al2O3 clusters

Heat dissipation has become a key problem for highly integrated and miniaturized electronic components. High thermal conductivity, good flowability and low coefficient of linear thermal expansion (CLTE) are indispensable performance parameters in the field of electronic potting composite materials. In this study, spherical alumina (Al₂O₃) was surface modified by γ-(2,3-epoxypropoxy) propyltrimethoxy silane (KH560) and γ-aminopropyltriethoxy silane (KH550) and labelled as Al₂O₃-epoxy and Al₂O₃–NH₂, respectively. Al₂O₃-epoxy and Al₂O₃–NH₂ powders were equally filled in vinyl silicone oil to prepare a high Al₂O₃ loading (89 wt%) precursor of silicone potting adhesive. The viscosity of the precursor rapidly decreased with increasing reaction time of Al₂O₃-epoxy and Al₂O₃–NH₂ at 140 °C. The viscosity reduction mechanism may be due to the formation of some Al₂O₃ clusters by the reaction of Al₂O₃-epoxy with Al₂O₃–NH₂, which results in some vinyl silicone oil segments being held in the channel of particles through capillary phenomenon, leading to the friction among Al₂O₃ clusters decreasing considerably. Laser particle size analysis and scanning electron microscopy (SEM) results confirmed the existence of Al₂O₃ clusters. Energy dispersive spectroscopy (EDS) and dynamic viscoelasticity experiments revealed that some segments of vinyl silicone oils were held by Al₂O₃ clusters. When Al₂O₃-epoxy and Al₂O₃–NH₂ reacted for 4 h, the thermal conductivity, CLTE and volume electrical resistivity of the silicone potting adhesive reached 2.73 W m⁻¹ k⁻¹, 75.8 ppm/°C and 4.6 × 10¹³ Ω cm, respectively. A new strategy for preparing electronic potting materials with high thermal conductivity, good flowability and low CLTE is presented.

Surface-modified Al₂O₃-epoxy reacts with Al₂O₃–NH₂ to form clusters that reduce the viscosity of electronic potting composites.     

Dual role of coal fly ash in copper ion adsorption followed by thermal stabilization in a spinel solid solution

Coal fly ash is usually used as a cost-effective adsorbent for heavy metal removal, accumulating large amounts of spent coal fly ash that requires further disposal. In this study, fly ash that adsorbs copper with a maximum copper adsorption capacity of 48.8 mg g⁻¹ was further sintered at 900–1050 °C, and it was found that the copper is thermally incorporated in a spinel structure in aluminum- and iron-containing ceramic matrices provided by the fly ash. To further explore the immobilization mechanisms of copper in both aluminum- and iron-containing ceramic matrices like those in fly ash, two systems were prepared from CuO + Fe₂O₃ + kaolinite and CuO + Fe₂O₃ + Al₂O₃. A CuAl_xFe_2−xO₄ spinel solid solution was formed, the peak intensity of which was found to increase upon an increase in the sintering temperature until a maximum amount was reached at 1150 °C. In the CuO + Fe₂O₃ + Al₂O₃ system, the 2θ value of the CuAl_xFe_2−xO₄ peaks was found to increase due to the continuous engagement of aluminum in the spinel structure. However, iron was found to be more likely to react with the copper in CuO + Fe₂O₃ + kaolinite during the formation of CuAl_xFe_2−xO₄. Through effective adsorption of copper on coal fly ash and the subsequent copper stabilization in the spinel, this study found a dual role for fly ash in copper immobilization and further confirmed the potential to recycle waste coal fly ash as a marketable ceramic material.

Coal fly ash is usually used as a cost-effective adsorbent for heavy metal removal, accumulating large amounts of spent coal fly ash that requires further disposal.     

Development of a thermally stable Pt catalyst by redispersion between CeO2 and Al2O3

For catalytic systems consisting of Pt as the active component and CeO₂–Al₂O₃ as the support material, the metal–support interaction between the Pt and CeO₂ components is widely applied to inhibit aggregation of Pt species and thus enhance the thermal stability of the catalyst. In this work, a highly thermostable Pt catalyst was prepared by modifying the synthesis procedure for conventional Pt/CeO₂/Al₂O₃ (Pt/Ce/Al) catalyst, that is, the CeO₂ component was introduced after deposition of Pt on Al₂O₃. The obtained CeO₂/Pt/Al₂O₃ (Ce/Pt/Al) catalyst exhibits significantly different aging behavior. During the hydrothermal aging process, redispersion of Pt species from the surface of Al₂O₃ to the surface of CeO₂ occurs, resulting in a stronger metal–support interaction between Pt and CeO₂. Thus, the formed Pt–O–Ce bond could act as an anchor to retard aggregation of Pt species and help Pt species stay at a more oxidative state. Consequently, excellent reduction capability and superior three-way catalytic performance are acquired by Ce/Pt/Al-a after hydrothermal aging treatment.

Ce/Pt/Al undergoes redispersion of Pt upon hydrothermal aging, resulting in higher dispersion and consequently superior three-way catalytic performance of Ce/Pt/Al-a.     

Keggin-structure heteropolyacid supported on alumina to be used in trans/esterification of high-acid feedstocks

Heteropolyacids (HPA) with Keggin structures, such as H₃PMo₁₂O₄₀ (H₃PMo), have been described as efficient catalysts in trans/esterification reactions due to their tolerance to water and free fatty acids contents, with particularly well-suited characteristics of high proton mobility and stability. The versatile array of HPA is considerably increased when such catalysts are supported onto solid matrices. In this sense, Al₂O₃ was assessed as support for H₃PMo to be used in trans/esterification reactions to produce biodiesel from high-acid feedstocks. The catalyst structure was characterized and applied on trans/esterification reaction of acid oils using ethanol as acyl acceptor. A face centered composite design was employed to conduct the experimental design and results analysis, taking macaw palm oil as study model. The process achieved an optimum level of 99.8% ester content and 4.1 mm² s⁻¹ viscosity under the following reaction conditions: 190 °C reaction temperature, 50 : 1 ethanol-to-oil molar ratio and 13.0% catalyst concentration. Other tested feedstocks (fungal single cell oil and residual frying oil) were also tested promoting satisfactory results, though the parameters were found to be slightly outside the limits set by the USA (ASTM D6715) standard. The H₃PMo/Al₂O₃ catalyst presented good regeneration and can be reused for up to four reaction cycles and requires lower ethanol-to-oil ratio, temperature, and catalyst concentration in comparison with other data from the literature.

Heteropolyacids (HPA) with Keggin structures, such as H₃PMo₁₂O₄₀ (H₃PMo), have been described as efficient catalysts in trans/esterifications of high-acid feedstocks due to their tolerance to water and free fatty acids contents.     

Synergistic advanced oxidation process for enhanced degradation of organic pollutants in spent sulfuric acid over recoverable apricot shell-derived biochar catalyst

The sulfuric acid-based alkylation process, which leads the industrial application market, still struggles with effectively removing a large number of organic pollutants from hazardous spent sulfuric acid. A synergistic advanced oxidation process was constructed to degrade the organic pollutants with H₂O₂ and sodium persulfate as the synergistic oxidants and apricot shell-derived biochar (OBC) as the catalyst. Taking the total organic carbon (TOC) and the color scale as the indices, the effects of critical experimental factors, i.e., reaction temperature, initial oxidant concentration, catalyst dosage, and aeration rate, were optimized. The results showed that the removal rates of TOC and the color of the spent sulfuric acid reached ∼91% and 96.6%, respectively, after 150 min under the optimum conditions. Besides, the efficient and low-cost OBC catalyst developed in this study could be continuously used for at least four times with about 75% TOC removal and 80% color removal, exhibiting favorable stability and good resistance to acid corrosion. Further study confirmed that the SO₄−˙ and ˙OH radicals generated in the synergistic advanced oxidation process strengthened the degradation and elimination of organic pollutants. The synergistic advanced oxidation process could provide a feasible insight for spent sulfuric acid treatment.

A synergistic advanced oxidation process was constructed to degrade the organic pollutants in spent sulfuric acid with apricot shell-derived biochar as the catalyst. It realized the effect of treating waste with waste.     

Conversion of levulinic acid to γ-valerolactone over Ru/Al2O3–TiO2 catalyst under mild conditions

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water. In this study, mixed oxides Al₂O₃–TiO₂, Al₂O₃–MoO₃ and Al₂O₃–Co₃O₄ were synthesized by co-precipitation using aqueous solution of NaOH as precipitant. Ru catalysts supported on mixed oxides were prepared by impregnation method and their catalytic performances were tested in the hydrogenation of LA to GVL on a fixed bed reactor. The physicochemical properties of the catalysts were characterized by XRD, H₂-TPR, NH₃-TPD, and BET techniques. The TiO₂ component significantly affected the acidity of the catalyst, and thus its catalytic activity for the GVL yield was affected. The desired product GVL with a yield of about 97% was obtained over the Ru/Al₂O₃–TiO₂ catalyst under mild conditions (WHSV = 1.8 h⁻¹, T = 80 °C). Moreover, the catalyst Ru/Al₂O₃–TiO₂ exhibited excellent thermal stability in the test period of time.

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water.     

Hydrodesulfurization of dibenzothiophene using Pd-promoted Co–Mo/Al2O3 and Ni–Mo/Al2O3 catalysts coupled with ionic liquids at ambient operating conditions

Sulfur compounds in fuel oils are a major source of atmospheric pollution. This study is focused on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) via the coupled application of 0.5 wt% Pd-loaded Co–Mo/Al₂O₃ and Ni–Mo/Al₂O₃ catalysts with ionic liquids (ILs) at ambient temperature (120 °C) and pressure (1 MPa H₂). The enhanced HDS activity of the solid catalysts coupled with [BMIM]BF₄, [(CH₃)₄N]Cl, [EMIM]AlCl₄, and [(n-C₈H₁₇)(C₄H₉)₃P]Br was credited to the synergism between hydrogenation by the former and extractive desulfurization and better H₂ transport by the latter, which was confirmed by DFT simulation. The Pd-loaded catalysts ranked highest by activity i.e. Pd–Ni–Mo/Al₂O₃ > Pd–Co–Mo/Al₂O₃ > Ni–Mo/Al₂O₃ > Co–Mo/Al₂O₃. With mild experimental conditions of 1 MPa H₂ pressure and 120 °C temperature and an oil : IL ratio of 10 : 3.3, DBT conversion was enhanced from 21% (by blank Ni–Mo/Al₂O₃) to 70% by Pd–Ni–Mo/Al₂O₃ coupled with [(n-C₈H₁₇)(C₄H₉)₃P]Br. The interaction of polarizable delocalized bonds (in DBT) and van der Waals forces influenced the higher solubility in ILs and hence led to higher DBT conversion. The IL was recycled four times with minimal loss of activity. Fresh and spent catalysts were characterized by FESEM, ICP-MS, EDX, XRD, XPS and BET surface area techniques. GC-MS analysis revealed biphenyl as the major HDS product. This study presents a considerable advance to the classical HDS processes in terms of mild operating conditions, cost-effectiveness, and simplified mechanization, and hence can be envisaged as an alternative approach for fuel oil processing.

Synergistic application of ionic liquids with Pd loaded Co–Mo@Al₂O₃ and Ni–Mo@Al₂O₃ catalysts for efficient hydrodesulfurization of dibenzothiophene at ambient conditions.     

Ultrasonic spray pyrolysis synthesis of TiO2/Al2O3 microspheres with enhanced removal efficiency towards toxic industrial dyes

Developing low-cost and highly effective adsorbent materials to decolorate wastewater is still challenging in the industry. In this study, TiO₂-modified Al₂O₃ microspheres with different TiO₂ contents were produced by spray pyrolysis, which is rapid and easy to scale up. Results reveal that the modification of γ-Al₂O₃ with TiO₂ reduced the crystallite size of Al₂O₃ and generated more active sites in the composite sample. The as-synthesized Al₂O₃–TiO₂ microspheres were applied to remove anionic methyl orange (MO) and cationic rhodamine B (RB) dyes in an aqueous solution using batch and continuous flow column sorption processes. Results show that the Al₂O₃ microspheres modified with 15 wt% of TiO₂ exhibited the maximum adsorbing capacity of ∼41.15 mg g⁻¹ and ∼32.28 mg g⁻¹ for MO and RB, respectively, exceeding the bare γ-Al₂O₃ and TiO₂. The impact of environmental complexities on the material''s reactivity for the organic pollutants was further delineated by adjusting the pH and adding coexisting ions. At pH ∼5.5, the TiO₂/Al₂O₃ microspheres showed higher sorption selectivity towards MO. In the continuous flow column removal, the TiO₂/Al₂O₃ microspheres achieved sorption capacities of ∼31 mg g⁻¹ and ∼19 mg g⁻¹ until the breakthrough point for MO and RB, respectively. The findings reveal that TiO₂-modified Al₂O₃ microspheres were rapidly prepared by spray pyrolysis, and they effectively treated organic dyes in water in batch and continuous flow removal processes.

Developing low-cost and highly effective adsorbent materials to decolorate wastewater is still challenging in the industry.     

Metal–support interaction induced ZnO overlayer in Cu@ZnO/Al2O3 catalysts toward low-temperature water–gas shift reaction

The water–gas shift reaction (WGSR) plays a pivotal role in many important industrial processes as well as in the elimination of residual CO in feed gas for fuel cells. The development of a high-efficiency low-temperature WGSR (LT-WGSR) catalyst has attracted considerable attention. Herein, we report a ZnO-modified Cu-based nanocatalyst (denoted as Cu@ZnO/Al₂O₃) obtained via an in situ topological transformation from a Cu₂Zn₁Al-layered double hydroxide (Cu₂Zn₁Al-LDH) precursor at different reduction temperatures. The optimal Cu@ZnO/Al₂O₃-300R catalyst with appropriately abundant Cu@ZnO interface structure shows superior catalytic performance toward the LT-WGSR with a reaction rate of up to 19.47 μmol_CO g_cat⁻¹ s⁻¹ at 175 °C, which is ∼5 times larger than the commercial Cu/ZnO/Al₂O₃ catalyst. High-resolution transmission electron microscopy (HRTEM) proves that the reduction treatment results in the coverage of Cu nanoparticles by ZnO overlayers induced by a strong metal–support interaction (SMSI). Furthermore, the generation of the coating layers of ZnO structure is conducive to stabilize Cu nanoparticles, accounting for long-term stability under the reaction conditions and excellent start/stop cycle of the Cu@ZnO/Al₂O₃-300R catalyst. This study provides a high-efficiency and low-cost Cu-based catalyst for the LT-WGSR and gives a concrete example to help understand the role of Cu@ZnO interface structure in dominating the catalytic activity and stability toward WGSR.

The water–gas shift reaction (WGSR) plays a pivotal role in many important industrial processes as well as in the elimination of residual CO in feed gas for fuel cells.     

Combined experimental and computational study of Al2O3 catalyzed transamidation of secondary amides with amines

Amides are the most extensively used substances in both synthetic organic and bioorganic chemistry. Unfortunately, the traditional synthesis of amides suffers from some important drawbacks, including low atom efficiency, high catalyst loading, separation of products from the reaction mixture and production of byproducts. Al₂O₃ is an amphoteric catalyst that activates the carbonyl carbon of the secondary amide group and helps the C–N cleavage of the reactant amide group by attacking the N–H hydrogen. By using the concepts of amphoteric properties of Al₂O₃, amides were synthesized from secondary amides and amines in the presence of triethylamine solvent. Several aliphatic and aromatic amines were used for the transamidation of N-methylbenzamide in the presence of the Al₂O₃ catalyst. Moreover, using the Gaussian09 software at the DFT level, HUMO, LUMO and the intrinsic reaction coordinates (IRCs) have also been calculated to find out the transition state of the reaction and energy. In this study, five successful compounds were synthesized by the transamidation of secondary amides with amines using a reusable Al₂O₃ catalyst. The catalyst was reused several times with no significant loss in its catalytic activity. The products were purified by recrystallization and column chromatography techniques. This catalytic method is effective for the simultaneous activation of the carbonyl group and N–H bond by using the Al₂O₃ catalyst.

Amides are the most extensively used substances in both synthetic organic and bioorganic chemistry.     

Mechanism of sulfidation of small zinc oxide nanoparticles

ZnO has industrial utility as a solid sorbent for the removal of polluting sulfur compounds from petroleum-based fuels. Small ZnO nanoparticles may be more effective in terms of sorption capacity and ease of sulfidation as compared to bulk ZnO. Motivated by this promise, here, we study the sulfidation of ZnO NPs and uncover the solid-state mechanism of the process by crystallographic and optical absorbance characterization. The wurtzite-structure ZnO NPs undergo complete sulfidation to yield ZnS NPs with a drastically different zincblende structure. However, in the early stages, the ZnO NP lattice undergoes only substitutional doping by sulfur, while retaining its wurtzite structure. Above a threshold sulfur-doping level of 30 mol%, separate zincblende ZnS grains nucleate, which grow at the expense of the ZnO NPs, finally yielding ZnS NPs. Thus, the full oxide to sulfide transformation cannot be viewed simply as a topotactic place-exchange of anions. The product ZnS NPs formed by nucleation-growth share neither the crystallographic structure nor the size of the initial ZnO NPs. The reaction mechanism may inform the future design of nanostructured ZnO sorbents.

In the sulfidation of small ZnO nanoparticles, the nanoparticles first undergo sulfur doping followed by the nucleation-growth of ZnS domains.

Zinc oxide (ZnO) nanoparticles (NPs), due to their cost-effectiveness and biodegradability, have a multitude of applications^1–3 including coatings^4–8 and pigments,^9,10 catalysis,^11,12 energy storage,^13,14 and environmental remediation.^15–22 ZnO NPs have particular appeal as sorbents for scavenging polluting sulfur compounds such as mercaptans and hydrogen sulfide (H₂S) from petroleum-based fuels:^23–27 ZnO + H₂S → ZnS + H₂O. Lattice O²⁻ in the ZnO is replaced with S²⁻ scavenged from the pollutant. Bulk powders of ZnO have already been used for adsorptive removal of H₂S,^28,29 but NPs have specific advantages. With smaller grain sizes, mass transport limitations are lifted.²³ Whereas sulfidation is limited to the surface of bulk ZnO, with NPs, the entire mass of ZnO can undergo sulfidation, enabling high sorbent capacity.²³ Volume and morphology changes resulting from restructuring of the solid can also be more easily accommodated with NPs,²³ allowing regenerable use of the sorbent. Finally, the high specific surface area of NPs allows more enhanced kinetics of the sulfidation reaction, potentially facilitating much lower desulfurization temperatures as compared to the conventional operating temperatures of 650–800 °C.^23,29In this context, small few-nm size ZnO NPs can be expected to be particularly promising, but it is important to understand the manner in which these NPs undergo sulfidation. The structural mechanism of the sulfidation process³⁰ may have critical differences compared to bulk ZnO powders or even larger NPs of tens of nm in size²⁴ and may therefore influence sorbent design. In a seminal study, Park et al.³⁰ studied the sulfidation of hexagonal-shaped 14 nm ZnO nanocrystals (NCs) at high temperature (235 °C) using hexamethyldisilathiane. The reaction was found to involve the anion exchange of O²⁻ with S²⁻ in the NC lattice. The overall shape and crystallography of ZnS NCs was templated by the initial ZnO NCs. However, due to the faster outward diffusion of Zn²⁺ as compared to the inward diffusion of S²⁻, the exchange reaction was accompanied by a nanoscale Kirkendall phenomenon, as a result of which the ZnS NCs formed were hollow.Here, we track the step-wise sulfidation of smaller (ca. 5 nm) ZnO NPs using optical spectroscopy and X-ray crystallography. Prior to the onset of sulfidation, O²⁻ in wurtzite ZnO NPs undergoes substitutional doping with S²⁻ without any major change in its structure. Upon reaching a critical concentration of sulfur doping, separate zincblende ZnS grains form and grow into ZnS NPs. Thus, the sulfidation of these small ZnO NPs studied here is not simply a topotactic or templated place-exchange of anions; rather the nucleation and growth of a separate ZnS crystallite is involved in the latter stages.     

The influence of composition on the functionality of hybrid CuO–ZnO–Al2O3/HZSM-5 for the synthesis of DME from CO2 hydrogenation

A series of CuO–ZnO–Al₂O₃/HZSM-5 hybrid catalysts with different Cu/Zn ratios and disparate Al₂O₃ doping were prepared and characterized by XRD, BET, H₂-TPR, NH₃-TPD and XPS techniques. The optimal Cu/Zn ratio is 7 : 3, and the introduction of a suitable amount of Al₂O₃ to form hybrid catalysts increased the BET specific area and micropore volume, facilitated the CuO dispersion, decreased the CuO crystallite size, increased the interaction between CuO and ZnO, enhanced the number of weak acid sites, altered the copper chemical state and improved the catalytic performance consequently. The highest CO₂ conversion, DME selectivity and DME yield of 27.3%, 67.1% and 18.3%, respectively, were observed over the CZA₇H catalyst. The suitable temperature of 260 °C and the appropriate space velocity of 1500 h⁻¹ for one-step synthesis of dimethyl ether (DME) from carbon dioxide (CO₂) hydrogenation were also investigated. The 50 h stability of the CZA₇H catalyst was also tested.

The introduction of Al₂O₃ increased the number of weak acid sites, altered the copper chemical state and improved the catalytic performance and stability consequently.     

Highly active and durable WO3/Al2O3 catalysts for gas-phase dehydration of polyols

Gas-phase glycerol dehydration over WO₃/Al₂O₃ catalysts was investigated. WO₃ loading on γ-Al₂O₃ significantly affected the yield of acrolein and the catalyst with 20 wt% WO₃ loading showed the highest activity. The WO₃/Al₂O₃ catalyst with 20 wt% WO₃ loading showed higher activity and durability than the other supported WO₃ catalysts and zeolites. The number of Brønsted acid sites and mesopores of the WO₃/Al₂O₃ catalyst did not decrease after the reaction, suggesting that glycerol has continuous access to Brønsted acid sites inside the mesopores of WO₃/Al₂O₃, thereby sustaining a high rate of formation of acrolein. Dehydration under O₂ flow further increased the durability of the WO₃/Al₂O₃ catalyst, enabling the sustainable formation of acrolein. In addition, the WO₃/Al₂O₃ catalyst with 20 wt% WO₃ loading showed high activity for the dehydration of various polyols to afford the corresponding products in high yield.

Gas-phase glycerol dehydration over WO₃/Al₂O₃ catalysts was investigated.     

Pt/Al2O3 coated with N-doped carbon as a highly selective and stable catalyst for catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline

Selective catalytic hydrogenation of p-chloronitrobenzene on Pt-based catalysts is a green and high-efficient way for p-chloroaniline production. However, supported monometallic Pt catalysts often exhibit undesirable p-chloroaniline selectivity. We herein reported supported Pt catalysts with N-doped carbon (NC) as an overcoating (Pt/Al₂O₃@NC) to overcome the disadvantage. Three Pt/Al₂O₃@NC catalysts with different NC coating amounts were prepared by in situ carbonization of an ionic liquid. For comparison, Al₂O₃ coated by NC and Pt/Al₂O₃ coated by SiO₂ were also prepared. A combination characterization confirmed that the NC overcoating was successfully formed on Pt/Al₂O₃ surface and Pt particles were completely coated by NC layers when ion liquid amount increased to 25 μl per g catalyst. Due to the intimate contact of NC layers and Pt particles Pt-NC heterojunctions were effectively formed on the catalyst surface. For the catalytic hydrogenation of p-chloronitrobenzene, Pt/Al₂O₃@NC with 25 μl ionic liquid as the NC precursor exhibited 100% selectivity to p-chloroaniline at 100% conversion of p-chloronitrobenzene. A lower ionic liquid amount led to decreased selectivity to p-chloroaniline. Furthermore, no deactivation was observed on Pt/Al₂O₃@NC during 5 catalytic cycles. The findings in the study demonstrate that coating noble metal catalysts by N-doped carbon is a promising method to enhance the selectivity and stability for catalytic hydrogenation of p-chloronitrobenzene.

Pt/Al₂O₃ with N-doped carbon overcoating exhibited 100% selectivity to p-chloroaniline for catalytic hydrogenation of p-chloronitrobenzene.     

Ultrasound-assisted coagulation for Microcystis aeruginosa removal using Fe3O4-loaded carbon nanotubes

Harmful cyanobacterial blooms are increasing environmental issues and require novel removal technology since the required doses of algaecides may cause further environmental pollution or treatment facility damage. Herein, we firstly introduce the combination of ultrasound and Fe₃O₄/CNTs as an alternative strategy to enhance coagulation for the removal of Microcystis aeruginosa cells in water. It remarkably enhanced cyanobacterial cell removal and microcystins control, compared with sonication alone (40 kHz ultrasonic bath, 4.2 mJ mL⁻¹). 94.4% cyanobacterial cells were removed using 20 second sonication with 20 mg L⁻¹ Fe₃O₄/CNTs, Al₂(SO₄)₃ coagulation (20 μM). Both sonication time and catalyst dose significantly influenced the cyanobacterial removal. Ultrasound with Fe₃O₄/CNTs only induced a slight increase of cell permeability, which may contribute to the effective control of DOC and microcystins'' release in water. The enhanced settlement of the cyanobacterial cells may result from the moderate oxidation on the cell surface. This study suggested a novel ultrasound-Fe₃O₄/CNT process to promote cyanobacteria removal with efficient DOC and microcystin release control, which is a green and safe technology for drinking water treatment.

The combination of sonication and Fe₃O₄/CNTs were applied on Microcystis aeruginosa removal for the first time.