Topics in Catalysis最新文献

Abstract

Crystal facet engineering is an effective strategy for designing efficient catalysts to improve the ability to oxidize formaldehyde (HCHO). In this article, anatase TiO₂ samples with different main exposed crystal facets ((001), (010) and (101)) were prepared and utilized as supports to load Pd, leading to the synthesis of Pd/TiO₂ (001), Pd/TiO₂ (010) and Pd/TiO₂ (101) catalysts, respectively. For HCHO oxidation, Pd/TiO₂ (001) displayed the best activity, and could convert 100% HCHO at 35 °C. However, the removal rates for Pd/TiO₂ (010) and Pd/TiO₂ (101) catalysts were only 46% and 35% even at 55 °C. After carefully comparing the property differences of these three supports, it was found that more surface defects were formed on the (001) facet than on (010) and (101). With more surface defects of support, Pd/TiO₂ (001) catalyst possessed more oxygen vacancies, Pd metal sites and interface sites, which could effectively activate oxygen and water. This further improved the ability to oxidize HCHO. The findings from this study are anticipated to contribute valuable insights for the design of highly efficient supported noble metal catalysts.

Abstract

MnO_X-Na₂WO₄/SiO₂ catalyst exhibited notable C₂ selectivity/yield in the oxidative coupling of methane (OCM), a promised green chemistry reaction. Nevertheless, the reaction mechanism of this catalyst remains a subject of contention, particularly regarding the role of Na₂WO₄ in the activation. In this study, in situ characterizations of a TiO₂-modified MnO_X-Na₂WO₄/SiO₂ catalyst are conducted by XRD and XPS correlating to the OCM reaction condition, focusing on the simultaneous phase transition of catalyst components within its activation temperature zone. The online MS along with XPS/XRD coupled activity study confirm that transition from Mn³⁺ to Mn²⁺ stands as a pivotal factor influencing the reactivity. In situ XRD further revealed that in this narrow temperature window there is a particular three-step Na₂WO₄ phase change, ending as molten salt, right before the substantial Mn³⁺ to Mn²⁺ transfer initiated. In addition, the rarely observed Na₂WO₄ behavior as molten salt is observed by in situ XPS with rapid spectra collected during an on-stage heating process. These comprehensive in situ catalyst characterizations, covering the extensive structure–activity relationship from solid state to partial molten salt condition, supply new important evidence of the active oxygen transfer pathway from Na₂WO₄ to Mn species which provides a key to understand the activation mechanism of MnO_X-Na₂WO₄/SiO₂ catalyst in OCM.

In the context of CO₂ valorisation, the reverse water–gas shift reaction (RWGS) is gathering momentum since it represents a direct route for CO₂ reduction to CO. The endothermic nature of the reaction posses a challenge when it comes to process energy demand making necessary the design of effective low-temperature RWGS catalysts. Herein, multicomponent Cs-promoted Cu, Ni and Pt catalysts supported on TiO₂ have been studied in the low-temperature RWGS. Cs resulted an efficient promoter affecting the redox properties of the different catalysts and favouring a strong metal-support interaction effect thus modulating the catalytic behaviour of the different systems. Positive impact of Cs is shown over the different catalysts and overall, it greatly benefits CO selectivity. For instance, Cs incorporation over Ni/TiO₂ catalysts increased CO selectivity from 0 to almost 50%. Pt-based catalysts present the best activity/selectivity balance although CuCs/TiO₂ catalyst present comparable catalytic activity to Pt-studied systems reaching commendable activity and CO selectivity levels, being an economically appealing alternative for this process.

Abstract

Selective and sensitive measurement of Prednisolone is vital for its routine analysis in pharmaceutical formulations and doping control in sports. In present research, an effective sensing platform for analysis of prednisolone in body fluids based on CuO@graphene nano-sized (Gr–CuO) catalyst was suggested. The electrochemical sensor was fabricated by deposition of the Gr–CuO on the GCE that provides a remarkably improved sensitivity for the square wave voltammetry detection of prednisolone drug. The uniform distribution of nano-sized CuO NPs led to superior electrocatalyst property, thereby maximizing the prednisolone determination abilities of the suggested sensor. The presented sensing strategy illustrates the acceptable linear response in the range of concentrations of 0.01–25 µM with a low detection limit of 0.008 µM owing to synergetic effect of Gr nanosheets and CuO NPs. The RSD value for prednisolone measurement using seven various GCEs was estimated as 3.4%. The anti-interference investigations confirmed that the different common biological interference such as glucose, dopamine, uric acid, ascorbic aide, xanthine and hypoxanthine did not affect the quantitative analysis of prednisolone. The validity of the Gr–CuO/GCE showed that the accurate detection of prednisolone in the body fluids of some athletes.

Pt-based alumina catalysts doped with varying niobium contents (i.e., 0, 1.20, 2.84, and 4.73 wt%, denoted as Pt/Nb–Al₂O₃) were synthesized via stepwise impregnation for catalytic CO oxidation. The effective incorporation of Nb species without altering the fundamental properties of the Al₂O₃ support was confirmed by the characterization using XRD, Raman, and TEM. Pt metallic particles were uniformly deposited on the niobium-doped alumina (Nb–Al₂O₃) support. H₂-TPR and CO–TPD analyses were performed to reveal the influence of niobium doping on catalyst reduction and CO adsorption properties. The results consistently demonstrate that the doping of niobium affects reducibility and alleviates the competitive adsorption between CO and O₂ during the CO reaction. Particularly, when compared to both undoped and excessively doped Pt/Al₂O₃ catalysts, the catalyst featuring a 2.84 wt% Nb content on Pt_1.4/Nb_2.8–Al₂O₃ displayed the most promising catalytic performance, with a turnover frequency of 3.12 s⁻¹ at 180 °C. This superior performance can be attributed to electron transfer at the Pt/NbOx interface.

Catalytic oxidation is an effective solution for the control of methane (CH₄) emission in exhausts from natural gas vehicles. Pd-based small-pore zeolites (such as Pd-SSZ-13) are considered to be the most active catalysts for CH₄ oxidation, but H₂O in the exhausts tends to induce deactivation of Pd catalysts. In this work, we tuned the hydrophobicity of Pd-SSZ-13 as a representative to improve its H₂O resistance in CH₄ oxidation. Pd-SSZ-13 catalysts with different Si/Al ratios were obtained by dealuminizing the pristine SSZ-13 zeolite with acid followed by Pd ion exchange, and a reduction of T₅₀ (i.e. the temperature to reach 50% conversion of CH₄) by 20 ℃ was achieved in CH₄ oxidation in the presence of 10 vol.% H₂O. Detailed physicochemical characterizations showed that the fraction of highly dispersed PdO species (highly active in CH₄ oxidation) increased, whereas that of less inactive PdO_x clusters decreased, in the Pd-SSZ-13 after acid modification. In addition, the increase of zeolite hydrophobicity after acid modification alleviated the H₂O inhibition effect on the active PdO phase, leading to a less activity loss of Pd-SSZ-13 in CH₄ oxidation. The improved hydrophobicity also favored C₃H₈ combustion over Pd-SSZ-13. These results suggested that simple acid modification could tune effectively the Si/Al ratio and hydrophobicity of zeolite supports, and eventually the physicochemical properties and oxidation performance of the supported Pd catalysts.

The photocatalytic properties of copper ferrites can be exploited in the degradation of organic contaminants in aqueous media, such as methylene blue. The interaction of ferrites with electromagnetic radiation results in the formation of chemical species capable of acting in the degradation of methylene blue molecules. The incorporation of these nanomaterials into geopolymeric matrices makes it possible to produce polymeric nanocomposites with improved properties. Geopolymers loaded with different percentages of copper ferrites were placed in contact with a solution of methylene blue, exposed to UV light and it was possible to observe photocatalytic activity in the degradation of this dye. Analysis in a UV–Vis spectrophotometer, at the maximum absorbance wavelength of the dye equivalent to 670 nm, showed that the geopolymer loaded with 2% copper ferrites was more effective in degrading methylene blue. These results display the potential of copper ferrite-loaded geopolymers as viable photocatalysts for organic pollutant remediation.

Abstract

Development of highly active and stable catalysts for production of CO_x-free hydrogen from ammonia is crucial for the use of ammonia as hydrogen carrier. Herein, Ru nanoparticles (NPs) on Nd₂O₃ (Ru/Nd₂O₃) was prepared by different methods and investigated for NH₃ decomposition reaction. The dependence of the catalytic activity of Ru NPs on the Nd₂O₃ on the interaction between Ru NPs and Nd₂O₃ support was investigated in detail. The Ru/Nd₂O₃ obtained from precipitation method exhibits a high hydrogen formation rate of 1548 mmol g_cat⁻¹ h⁻¹ at 450 °C, which is high than that of the Ru/Nd₂O₃ analogue from milling method and comparable with many efficient oxides supported Ru catalysts reported previously. As revealed by various characterization techniques, the high activity of Ru/Nd₂O₃ obtained from precipitation method can be attributed to the enhanced interaction between Ru NPs and Nd₂O₃. The Ru NPs in Ru/Nd₂O₃ analogue with enhanced the metal-support interaction can modulate electronic structure and facilitate the activation and decomposition of NH₃. Therefore, Ru/Nd₂O₃ obtained from precipitation method exhibited significantly improved activity and intrinsic activity for NH₃ decomposition. This study provides promise for the design of efficient Ru/Nd₂O₃ catalyst for NH₃ decomposition reaction by tuning the metal–support interaction of catalysts.

Biodiesel stands out as a promising contender in the quest for renewable energy solutions, offering a greener alternative to traditional fossil fuels. Derived primarily from the transesterification of vegetable oils or animal fats, biodiesel offers an eco-friendly energy avenue with a minimized carbon footprint. Catalysts are central to the success of this process, which significantly enhance yield rates. Geopolymers, traditionally associated with construction applications due to their inorganic nature, have been derived from aluminosilicate sources activated using alkaline solutions. However, recent advancements spotlight geopolymers in a new light, emphasizing their prospective role as nanocatalytic agents for biodiesel synthesis. This paradigm shift suggests improved production efficiency and an innovative method of repurposing industrial waste. This study centers on the pioneering application of geopolymers, fortified with magnetite, as potent heterogeneous catalysts for biodiesel generation from soybean and safflower oils. By leveraging a meticulously crafted geopolymer matrix—consisting of metakaolin, sodium hydroxide, and magnetite—this research replaced traditional catalysts with this advanced nanostructured geopolymer variant in the biodiesel methylation process. The research delved deep to ascertain the prime synthesis conditions. Furthermore, utilizing cutting-edge machine learning methodologies provided an analytical lens to navigate the extensive experimental data, thereby fine-tuning the optimization trajectory. One of the salient takeaways from this research is the validation that geopolymer catalysts, rooted in kaolinite, can be ingeniously tailored to ensure elevated biodiesel yields across a spectrum of oil sources, underscoring their unparalleled efficiency and versatility in the biofuel domain.