Effects of Ti loading on activity and redox behavior of metals in PtCeTi/KIT-6 catalysts for CH4 and CO oxidation

Variation in Metal-Support Interaction with TiO2 Loading and Synthesis Conditions for Pt-Ti/SBA-15 Active Catalysts in Methane Combustion

The control of catalytic performance using synthesis conditions is one of the main goals of catalytic research. Two series of Pt-Ti/SBA-15 catalysts with different TiO₂ percentages (n = 1, 5, 10, 30 wt.%) were obtained from tetrabutylorthotitanate (TBOT) and peroxotitanate (PT), as titania precursors and Pt impregnation. The obtained catalysts were characterized using X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), N₂ sorption, Raman, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), hydrogen temperature-programmed reduction (H₂-TPR) and H₂-chemisorption measurements. Raman spectroscopy showed framework titanium species in low TiO₂ loading samples. The anatase phase was evidenced for samples with higher titania loading, obtained from TBOT, and a mixture of rutile and anatase for those synthesized by PT. The rutile phase prevails in rich TiO₂ catalysts obtained from PT. Variable concentrations of Pt⁰ as a result of the stronger interaction of PtO with anatase and the weaker interaction with rutile were depicted using XPS. TiO₂ loading and precursors influenced the concentration of Pt species, while the effect on Pt nanoparticles' size and uniform distribution on support was insignificant. The Pt/PtO ratio and their concentration on the surface were the result of strong metal-support interaction, and this influenced catalytic performance in the complete oxidation of methane at a low temperature. The highest conversion was obtained for sample prepared from PT with 30% TiO₂.

Au/Ti Synergistically Modified Supports Based on SiO2 with Different Pore Geometries and Architectures

New photocatalysts were obtained by immobilization of titanium and gold species on zeolite Y, hierarchical zeolite Y, MCM-48 and KIT-6 supports with microporous, hierarchical and mesoporous cubic structure. The obtained samples were characterized by X-ray diffraction (XRD), N2-physisorption, scanning and transmission electron microscopy (SEM/TEM), diffuse reflectance UV–Vis spectroscopy (DRUV-Vis), X-ray photoelectron spectroscopy (XPS), Raman and photoluminescence spectroscopy. The photocatalytic properties were evaluated in degradation of amoxicillin (AMX) from water, under UV (254 nm) and visible light (532 nm) irradiation. The higher degradation efficiency and best apparent rate constant were obtained under UV irradiation for Au-TiO2-KIT-6, while in the visible condition for the Au-TiO2-MCM-48 sample containing anatase, rutile and the greatest percent of Au metallic clusters were found (evidenced by XPS). Although significant values of amoxicillin degradation were obtained, total mineralization was not achieved. These results were explained by different reaction mechanisms, in which Au species act as e− trap in UV and e− generator in visible light.

Nanofiltration Composite Membranes Based on KIT-6 and Functionalized KIT-6 Nanoparticles in a Polymeric Matrix with Enhanced Performances

The nanofiltration composite membranes were obtained by incorporation of KIT-6 ordered mesoporous silica, before and after its functionalization with amine groups, into polyphenylene-ether-ether-sulfone (PPEES) matrix. The incorporation of silica nanoparticles into PPEES polymer matrix was evidenced by FTIR and UV–VIS spectroscopy. SEM images of the membranes cross-section and their surface topology, evidenced by AFM, showed a low effect of KIT-6 silica nanoparticles loading and functionalization. The performances of the obtained membranes were appraised in permeation of Chaenomeles japonica fruit extracts and the selective separation of phenolic acids and flavonoids. The obtained results proved that the PPEES with functionalized KIT-6 nanofiltration membrane, we have prepared, is suitable for the polyphenolic compound’s concentration from the natural extracts.

Synthesis of mesoporous ZnO/TiO2-SiO2 composite material and its application in photocatalytic adsorption desulfurization without the addition of an extra oxidant

Photocatalytic adsorption desulfurization (PADS) technology has attracted enormous attention in the deep desulfurization field. Therefore, a good material with high photocatalytic activity and adsorption capacity toward organic sulfide is desirable. Herein, mesoporous ZnO/TiO2-SiO2 (ZTS) was synthesized for the first time and successfully applied in the photocatalytic desulfurization of dibenzothiophene (DBT). The composite materials were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), N2-physisorption, transmission electron microscopy (TEM), UV-Vis diffusive reflectance spectra (UV-Vis DRS), X-ray photo-electron spectroscopy (XPS), photoluminescence (PL) and electron spin resonance (ESR). The results show that the doping of TiO2 promotes the photocatalytic and adsorption abilities of the catalysts dramatically. ZTS-3 with Si/Ti = 3 exhibits the best photocatalytic desulfurization activity compared with other proportions of titanium doping. The final DBT conversion can reach 97%, and the maximum adsorption of DBT over ZTS-3 is 47 mg-S per g-cat. The photocatalytic test indicates that the remarkable photocatalytic activity of ZTS is due to the formation of a heterojunction by the interaction of ZnO and TiO2, which can successfully expand solar light absorption, improving the charge separation efficiency and inhibiting the recombination of photocatalytic electron-hole pairs. Moreover, no extra oxidants (such as O2, H2O2 or an organic oxidant) were added, which is highly beneficial for the consequent treatment of the fuel and can reduce the processing cost markedly.

Recent advances in three-way catalysts of natural gas vehicles

This review presents recent advances in TWCs for NGVs, particularly for Pd-based catalysts and potential alternatives.

Suppressing Ammonia Re-Emission with the Aid of the Co3O4-NPs@KIT-6 Catalyst in Ammonia-Based Desulfurization

The re-emission of NH₃ and SO₂ caused by the decomposition of (NH₄)₂SO₃ is a crucial concern in ammonia-based desulfurization. In this study, a novel Co₃O₄-NPs@KIT-6 catalyst with a three-dimensional two-helix structure is proposed for converting (NH₄)₂SO₃ into (NH₄)₂SO₄. The oxidation rate of (NH₄)₂SO₃ with the catalyst was 7.5 times that without any catalyst, and this improvement was attributed to appropriately dispersed Co₃O₄ nanoparticles with a size of 4-10 nm that interacted with the KIT-6 support. Therefore, the number of active sites with substitution and hole defects was substantially increased, which is advantageous for high catalytic activities. Consequently, the amount of NH₃ and SO₂ re-emission during (NH₄)₂SO₃ oxidation was reduced by 43.9%, which considerably reduced potential environmental risks. The results of this study serve to advance ammonia desulfurization by improving the desulfurization efficiency, downsizing the oxidation tank, and generating considerable profit from efficient reclaiming of (NH₄)₂SO₄ as a fertilizer.

Effect of Preparation Method of Co-Ce Catalysts on CH4 Combustion

Transition metal oxides have recently attracted considerable attention as candidate catalysts for the complete oxidation of methane, the main component of the natural gas, used in various industrial processes or as a fuel in turbines and vehicles. A series of novel Co-Ce mixed oxide catalysts were synthesized as an effort to enhance synergistic effects that could improve their redox behavior, oxygen storage ability and, thus, their activity in methane oxidation. The effect of synthesis method (hydrothermal or precipitation) and Co loading (0, 2, 5, and 15 wt.%) on the catalytic efficiency and stability of the derived materials was investigated. Use of hydrothermal synthesis results in the most efficient Co/CeO2 catalysts, a fact related with their improved physicochemical properties, as compared with the materials prepared via precipitation. In particular, a CeO2 support of smaller crystallite size and larger surface area seems to enhance the reducibility of the Co3O4/CeO2 materials, as evidenced by the blue shift of the corresponding reduction peaks (H2-TPR, H2-Temperature Programmed Reduction). The limited methane oxidation activity over pure CeO2 samples is significantly enhanced by Co incorporation and further improved by higher Co loadings. The optimum performance was observed over a 15 wt% Co/CeO2 catalyst, which also presented sufficient tolerance to water presence.