Topics in Catalysis最新文献

Heavy-duty and marine transport will continue to rely on robust, high energy–density, combustion engine technology. Sustainable fuels, fuel-flexible engines and stricter future emission standards all call for further development of catalytic aftertreatment systems (ATSs). This paper reviews progress and evaluates emission removal methods, based on synthetic gas bench (SGB) experiments simulating characteristic lean and stoichiometric conditions in hydrogen, ammonia, methanol and methane engine exhaust gases. The oxidation reactivity of fuel compounds on tailored catalysts showed the following light-off temperatures (T₅₀, °C) in lean conditions: hydrogen(140) < methanol(170) ~ CO < diesel-hydrocarbons, reference(180) < ammonia(250) < methane(380). NO_x removal in mobile applications will be challenging, due to NO_x limits and varying fuel types/mixtures. Urea/NH₃-SCR will remain the main NO_x removal method, with an option of double SCR widening its temperature window. NO_x storage catalysts based on metal oxides or zeolites, increased NO_x removal at 100–200 °C by passive adsorption–desorption. NO_x reduction by hydrogen (H₂-SCR) showed NO_x reduction of up to 60–70% on platinum catalysts at 100–160 °C, before NH₃-SCR reactions at higher temperatures. Selective ammonia slip catalysts (ASCs) were effective to cut NH₃ emissions. High selectivity to N₂ with low N₂O formation was challenging with H₂-SCR and ASC. Three-way catalysts, applied with stoichiometric hydrogen combustion, were operating below 200 °C. More efficient catalytic methods for methane and N₂O removal are required to improve the feasibility of methane and ammonia as future fuels. Integration of different properties in the same units is essential to minimise ATS volume and costs. The flexible use of green fuels requires flexible ATSs too.

A coaxial dielectric barrier discharge (DBD) as a non-thermal plasma reactor was utilized for the non-oxidative coupling of methane into higher hydrocarbons under ambient conditions. The DBD reactor was subsequently performed as a packed-bed dielectric barrier discharge using non-catalytic materials, including glass beads, glass wool, and glass capillary, which were introduced to investigate the non-catalytic reaction mechanism. Typical observation demonstrated that the dielectric glass materials packed with DBD might successfully activate the stable C–H bond to produce hydrogen and C₂–C₄ higher hydrocarbons without the application of any oxidants and additional thermal energy. Among the packing materials investigated, the DBD reactor packed with a glass capillary obtained a maximum CH₄ conversion of 6.1%, with the energy efficiency reaching a maximum of 0.66 mmol kJ⁻¹ at a discharge power of 1.38 W with an SEI of 4.14 J mL⁻¹. The enhanced CH₄ conversion was attributed to an alternation in the plasma discharge behavior with non-catalytic glass materials. Moreover, under these conditions, the low temperature of the discharge zone resulted in minimal solid carbon accumulation on the inner electrode surface of the plasma reactor.

Oxygen vacancy defects can serve as an effective strategy for developing high-performance metal oxide-based catalysts. The formation of oxygen vacancies depends on the reducibility of the metal oxide materials. In this study, we selected three metal oxides (MO_xs): iron oxide (Fe₂O₃), chromium oxide (Cr₂O₃), and zirconium oxide (ZrO₂), with varying degrees of reducibility to investigate oxygen vacancy formation and its consequent impact on platinum (Pt) dispersion and catalytic performance. An oxy-hydrogen flame treatment, characterized by high treatment temperatures and rapid heating and cooling rates, was employed to create oxygen vacancy defects in these metal oxides. The flame treatment promoted defect formation in the order of Fe₂O₃ > Cr₂O₃ > ZrO₂. These defects significantly influenced Pt dispersion and metal-support interactions. The catalytic performance of Pt/MO_x catalysts, both untreated and treated with the oxy-hydrogen flame, was evaluated in the chemoselective hydrogenation of 3-nitrostyrene. The selectivity toward 3-vinylaniline increased with the reducibility of the metal oxide support in the defective Pt/MO_x catalysts. Higher reducibility facilitated oxygen vacancy formation, enhanced Pt dispersion through metal-support interactions, and ultimately improved chemoselective hydrogenation performance.

Metal support interaction (MSI) and oxygen vacancies have a significant impact on the performance of the Ni catalyst for dry reforming of methane (DRM) reaction. In this paper, the synergistic effect between chelating agents and dielectric barrier discharge (DBD) technology was systematically investigated by adding different chelating agents and combining with DBD during the catalyst preparation process. The introduction of the chelating agents improved the dispersion of Ni species exposing more active sites to participate in the reaction. On this basis, DBD technology significantly increased the number of oxygen vacancies on the catalyst surface while further strengthening the MSI by reducing the size of Ni nanoparticles. Notably, ethylene glycol and DBD demonstrated excellent synergistic effects in promoting the activity, stability, and carbon resistance of Ni catalysts, which could be related to the relative content of NiAl₂O₄ in catalysts. This research makes a substantial contribution to enhancing the reactivity of DRM catalyst by using chelating agents and DBD to alter the MSI and increase the number of oxygen vacancies.

Crystalline MoVTe(Sb)NbO oxide catalysts have been shown to exhibit high oxidation catalytic performance in propane ammoxidation. However, the roles of individual elements remain unclear. In order to elucidate these elemental roles, Nb and Te were introduced into the orthorhombic Mo₃VO_x oxide (Orth-MoVO) through post-hydrothermal treatment. Structural analysis revealed that Nb covers the surface of the Orth-MoVO crystal particles, while Te is accommodated within the hexagonal channel of the orthorhombic structure. Physicochemical characterization demonstrated that Nb enhance the structural stability of the orthorhombic phase, and the introduction of Te into amorphous Mo₃VO_x oxide through post-hydrothermal treatment facilitated crystallization from the amorphous phase to the orthorhombic structure during heat treatment. These findings provide novel insights into the roles of individual elements in Mo-V-Te(Sb)-Nb oxide catalysts.

This work employed a novel, easy, and environmentally friendly method for synthesizing platinum nanoparticles over a multi-walled carbon nanotubes (CNT_f) surface, employing thiophene (TH) as a reducing agent and stabilizer. The nanoparticle size depends on Pt concentration and TH to be employed as counter electrodes in the I⁻/I₃⁻ reduction reaction and compared with the traditional Pt counter electrode. The fabricated counter electrodes were evaluated in dye-sensitized solar cells (DSSCs). The results indicate Pt₂/CNT_f hybrid material counter electrode presents a charge transfer resistance (R_CT) of 4.20 Ω, and the photovoltaic parameters of the cell were Jsc = 11.23 (mA/cm²); V_OC = 0.781 V, and FF = 60.6, with an efficiency of 5.32%. The traditional Pt counter electrode shows an (R_CT) of 8.65 Ω, and the photovoltaic parameters of the cell were Jsc = 11.37 (mA/cm); V_OC = 0.769 V and FF = 64.5, with an efficiency of 5.94%. The Pt₂/CNT_f hybrid material performs similarly to traditional Pt counter electrodes, but the Pt₂/CNT_f hybrid presents five times less Pt concentration.

This study reports the hydrothermal synthesis, comprehensive characterization, and catalytic evaluation of zirconia nanoparticles with various phases for chemoselective reduction of α-keto esters & amides. These nanoparticles exhibited remarkable catalytic activity in highly chemoselective reduction reactions in which monoclinic zirconia NP’s show excellent efficiency, particularly in the reduction of α-keto esters and amides utilizing NaBH₄ as the reductant and methanol/ethanol as environmentally benign solvents. A significant advancement is demonstrated through the achievement of 83–99% conversions for α-hydroxy esters and α-hydroxy amides in a remarkably short time frame of 20–25 min. Furthermore, the ZrO₂ nano-catalyst demonstrates remarkable reusability, maintaining catalytic activity through five consecutive cycles without significant decline. A combination of FE-SEM, XRD, EDX-elemental mapping, FTIR, BET analysis, and Ammonia TPD techniques was employed to investigate the morphology, thermal stability, crystal structure, and surface acidity of fresh ZrO₂ NP’s. The TPD results reveal that M-ZrO₂ exhibits superior acidic properties compared to T-ZrO₂.

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While the temperature-programmed desorption of ammonia (NH₃-TPD) is widely used to analyze the combined Lewis and Brønsted acidity of heterogeneous catalysts, the temperature-programmed desorption of isopropylamine (IPAm-TPD) can be used for the selective analysis of Brønsted acidity. This work compared NH₃-TPD and IPAm-TPD as analysis methods for the acidity of zeolitic samples, including H-ZSM-5-23, H-ZSM-5-50, H-ZSM-5-280, a Zn-modified H-ZSM-5-50 sample, and a γ-Al₂O₃ reference sample. For the unmodified H-ZSM-5-23, H-ZSM-5-50, and H-ZSM-5-280, the total acidity determined with NH₃-TPD remained higher and the Brønsted acidity determined with IPAm-TPD lower than the theoretical acidity estimated with the Al content of the materials. When the NH₃-TPD saturation temperature was varied for H-ZSM-5-50 to examine the trends observed in the analyses, the temperature change affected primarily the low temperature peak of the TPD traces. The Zn-modified Zn/H-ZSM-5-50 sample yielded a multi-peak IPAm-TPD trace, though only a single peak trace was expected. Additionally, the value of Brønsted acidity showed no change from the unmodified zeolite.

Various compositions of silica-supported manganese-copper mixed oxide catalysts were explored for the aerobic oxidation of cyclohexane with molecular oxygen as the oxidant. The investigated SiO₂–MnO_x–CuO catalysts with varying weight ratios were prepared by the wet-impregnation method. The prepared catalysts were characterized by various techniques such as XRD, XPS, N₂-physisorption, SEM, and HR-TEM. Among the prepared catalysts, the SiO₂-MnO_x–CuO (SMC964) combination catalyst showed superior catalytic activity with 96% conversion and 96% allylic selectivity (85% selectivity to 2-cyclohexene-1-one and 11% selectivity to 2-cyclohexene-1-ol). Compared to pure metal oxides, the silica-supported mixed metal oxide catalysts demonstrated superior catalytic performance due to high surface area, mixed metal oxide nanoparticles forming on the support, and synergetic interaction between the metal oxides and the support. The influence of different reaction parameters, including the effect of solvent, temperature, reaction time, and catalyst amount, was systematically studied to optimize the reaction conditions. Furthermore, reusability tests over five cycles revealed excellent catalyst stability with negligible loss in activity.

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