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Noble metal‐free catalyst or catalytic oxidation of 5‐hydroxymethylfurfural into 2,5‐furandicarboxylic acid are proposed in this study as a proposal to solve one of the great disadvantages of this reaction of using preferably noble metal‐based catalysts. The catalytic activity of six MnO2 crystal structures is studied as alternative. The obtained results showed a strong connection between catalytic activity the type of MnO2 structure organization and redox behavior. Among all tested catalysts, ϵ‐MnO2 showed the best performance with an excellent yield of 74 % of 2,5‐furandicarboxylic acid at full ‐hydroxymethylfurfural conversion. [ABSTRACT FROM AUTHOR]

This study is focused on the design control of Cu–Zr–Ti oxide composites by the variation of the Zr/Ti ratio and the copper deposition procedure used. For the first time, these ternary composites were obtained by a combination of template-assisted hydrothermal techniques for the preparation of mesoporous ZrO2–TiO2 mixed oxides with diverse compositions, followed by the consecutive chemisorption and hydrolysis of copper ammonia complexes on them. The nitrogen physisorption, XRD, SEM, HRTEM, TPR, XPS, UV-Vis, and Raman spectroscopies were applied for the catalysts' characterization. Methanol decomposition and the total oxidation of ethyl acetate, both of which with potential for sustainable environmental protection, were used as catalytic tests. The complex relationship between the phase composition, structure, and morphology of titania–zirconia mixed oxides and the state and catalytic behavior of the copper oxide species supported on them was investigated. In comparison with the conventional impregnation technique, the novel preparation procedure revealed the generation of more uniform and homogeneously dispersed needle-like copper oxide crystallites in the mesoporous TiO2–ZrO2 host matrix, which typically ensure improved catalytic performance. The synergistic activity between the loaded copper species and TiO2–ZrO2 support was discussed. All ternary composites exhibited superior catalytic activity in total oxidation of ethyl acetate. The specific behavior of the catalysts in methanol decomposition was related to the irreversible phase transformations by the influence of the reaction medium. [ABSTRACT FROM AUTHOR]

Abstract: Au/Nb2O5 and Au/CeO2 catalysts were studied for the selective hydrogenation of crotonaldehyde, both in liquid (batch reactor, 4atm, 60°C, solvent: isopropanol) and in gas (flow microreactor, 120°C, atmospheric pressure) phases. Samples were characterized by TPR and XRD and tested for the CO oxidation reaction. Large differences in support reducibility between both catalysts were determined from the TPR results. The XRD and CO oxidation results demonstrated that the gold particles were lower than 5nm. The dependence of the selectivity towards crotyl alcohol and of the conversion on time on stream was measured. The niobia-supported catalyst was mainly unselective, the selectivity towards crotyl alcohol value being 20% for both liquid and gas phases. The Au/CeO2 catalyst is highly selective in gas phase (78% of selectivity towards crotyl alcohol). Under liquid phase conditions, a high selectivity level was not reached mainly due to secondary reactions. [Copyright &y& Elsevier]

SnO2/Fe2O3 nanocomposites have been prepared over the entire composition range (0–100 mol% Fe2O3) through precipitation from solution, and their ethanol-sensing performance (10–200 ppm C2H5OH) was evaluated using electrical conductivity measurements in the temperature range 150–450°C. The sensing performance of the nanocomposites is shown to strongly depend on their composition. The Fe2O3-rich (>70 mol% Fe2O3) nanocomposites offer a large C2H5OH response and low sensitivity to ambient humidity. The oxidizing and acid properties of the nanocomposites have been studied using temperature-programmed hydrogen reduction and ammonia desorption measurements, and their catalytic activity for oxidation of ethanol was assessed by gas chromatography mass spectrometry in a flow system. The results indicate that increasing the Fe2O3 content of the nanocomposites reduces the density of acid centers on their surface and enhances their activity for oxidation of ethanol. [ABSTRACT FROM AUTHOR]

Abstract: This paper is devoted to the development of a low-dimensional kinetic model of CO oxidation on a metallic catalyst surface and theoretical study of arising nonlinear phenomena and relaxation oscillations of the reaction rate. Experimental results of studies on the adsorbed oxygen are presented and its significance in the CO oxidation mechanism on Ir catalyst is shown. We consider the conventional Langmuir–Hinshelwood mechanism of catalytic CO oxidation and take into account the possibility of a metallic surface modification during reaction due to the oxygen penetration into subsurface layers. We suggest that when the adsorbed oxygen concentration exceeds some critical value, a surface modification occurs and the reaction capability of adsorbed oxygen changes, so that the activation energy of the interaction between the adsorbed species sharply increases. Construction of bifurcation curves on the parametric plane (P CO, ) permits us to separate areas of CO and O2 partial pressures, for which self-oscillations and/or multiplicity of steady states appear. This paper deals with parametric analysis of a new two-variable kinetic model of CO oxidation on Ir catalyst surface, but the approach developed is rather general and can be applied to studies of different catalytic reactions. [Copyright &y& Elsevier]

BET, XRD, XPS, and TPR by hydrogen were used for investigation of supported Mn–Bi oxide catalysts for ammonia oxidation into nitrous oxide. The catalysts were synthesized by impregnation of γ-, α-Al2O3 and SiO2 with solutions of manganese and bismuth nitrates. The character of phase transformations, surface concentration, and state of the active component were shown to depend on the nature of the support. The sequence stabilization of active constituents of the Mn–Bi–O/α-Al2O3 catalyst and types of the stabilized species were determined. The activity of the Mn–Bi–O supported catalysts calcined at 400 °C was established to equal 95–97% and to be practically independent of the support nature, while the activity decreased with elevation of the calcination temperature. The Mn–Bi–O/α-Al2O3 catalysts exhibited the highest selectivity to N2O (84.4%) under identical conditions. The correlation between the Mn3+/Mnδ+ (2<δ<3) ratio in the catalyst and the selectivity to N2O was revealed. [Copyright &y& Elsevier]

New carbonized biomass–metakaolin (PSD/MK_Fe) granular composite catalyst materials were manufactured for the catalytic wet air oxidation (CWAO) of bisphenol A (BPA). These catalysts were characterized using different analytical and spectroscopic techniques, and results showed that the catalysts' final properties were influenced by the addition of metakaolin (MK), polyvinyl alcohol, boric acid, and iron. Under the optimal CWAO experimental conditions (p: 20 bar, T: 160 °C, initial pH: 5–6, c[catalyst]: 1.0 g/L), nearly complete BPA conversion (>98%) and total organic carbon (TOC) conversion of 70% were reached. A key factor behind the enhanced catalytic activity was high specific surface area, although catalytic activity was also affected by surface acidity. These results confirmed the high efficiency of the current BPA conversion process involving the use of the easily separable and reusable PSD/MK_Fe catalyst. Therefore, biomass composite catalysts can be regarded as efficient catalysts for the oxidation of BPA during the CWAO process. [ABSTRACT FROM AUTHOR]

• 100% FDCA yield is achieved at low temperature and base concentration over Au/Al 2 O 3 catalyst. • Full HMF conversion in less than 10 min. • Catalyst stable under recycling conditions with slight deactivation after 5 runs. • CeO 2 (20 wt.%) introduction promotes HMF/intermediates oxidation. The catalytic activity of a simple Au/Al 2 O 3 catalytic system prepared by the direct anionic exchange (DAE) method was evaluated in the selective 5-hydroxymethylfurfural (HMF) oxidation under mild conditions, using molecular oxygen as the oxidant. The influence of the HMF/NaOH ratio and reaction time on product yield and distribution were studied and discussed in detail. Extremely high activity and selectivity were observed in mild conditions, with 99% of 2,5-furandicarboxylic acid (FDCA) production at full HMF conversion after 4 h with the use of only 4 equivalents of NaOH at 70 °C. Catalyst viability and stability were verified by repeating the cycle up to five times. Changes in the nature of the support were also contemplated by introducing some ceria fraction, i.e. 20 wt%. [ABSTRACT FROM AUTHOR]

Alumina supported catalysts comprised of a ceria–zirconia solid solution and lanthanum nickelate promoted by Pt were tested in the partial oxidation of methane into synthesis gas under conditions (high temperature, short contact time, highly diluted gas mixture, small catalyst grains) providing acquisition of a catalyst intrinsic activity. The phase composition and reducibility of catalysts were characterized with XRD and TPR. The influence of the catalyst chemical composition, type of redox pretreatment and support phase composition on the activity has been studied. Prolonged relaxations of catalytic activity have been observed, and their nature is discussed taking into account the catalyst properties. [Copyright &y& Elsevier]

Highlights: [•] Development of efficient catalysts for both WGS and PrOx reactions. [•] Extensive study of the PrOx reaction parameters to achieve the best activity/selectivity ratio. [•] CO/H2 pulses study for understanding of H2/CO oxidation competition. [•] Suitability of the samples in the PrOx reaction especially under high CO inlet concentrations. [ABSTRACT FROM AUTHOR]