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The valorization of greenhouse gases, especially when focused on carbon dioxide, currently belongs to the main challenges of pro-environmental chemical processes. One of the important technologies in this field is dry methane reforming (DMR), leading to the so-called synthesis gas (CO + H2). However, to be efficient and economically viable, an active and stable catalyst is required. Ni-based systems can be recommended in this regard. This research aimed to investigate how nickel content can influence the activity of model NiOx/CeO2 catalysts in DMR. A series of NiOx/CeO2 samples of various nickel loadings (0–10 wt.%) were prepared through dry impregnation. The obtained samples were characterized through XRD, RS, N2-BET, DRIFT, SEM, UV/Vis-DR, and XPS. Nonlinear changes in surface properties of the investigated samples with increasing nickel concentration were found. The observed changes are mirrored both in the determined nickel speciation and in the corresponding catalytic activity. The highest activity was found for the catalyst containing 3 wt.%. of nickel. [ABSTRACT FROM AUTHOR]

Catalytic performance of 3 and 5 wt.% of vanadia, supported on zirconia, zirconia-ceria, and zirconia-yttria, tested in the combustion of soot without and in the presence of NO was described. The catalysts were characterized by structural (XRD, RS) and functional (EPR, TPR) methods. The effect of composition on the catalytic performance of the investigated systems in soot combustion was discussed in detail. Zirconia-supported vanadia was found to be the most active catalyst for soot oxidation characterized by the lowest combustion temperature (~375 °C) attributed to the maximal signal of conversion to the detected products. The relationship between the reducibility of surface oxovanadium species and their catalytic activity was established, revealing the involvement of the lattice oxygen in the combustion process. The importance of thermal treatment conditions and the nature of zirconia-based support determining the stability of specific oxovanadium entities on the catalyst surface was emphasized. [ABSTRACT FROM AUTHOR]

A series of MoO3/ t-ZrO2 catalysts was prepared by slurry deposition. Structural studies revealed that the presence of MoO3 had no influence on the phase composition of zirconia support. IR/RS and EPR results confirmed that both isolated and polymeric (2D) oxomolybdenum species occurred on catalysts surface. Adsorption of NO resulted in the reduction of molybdenum centers with simultaneous formation of surface nitrates. [ABSTRACT FROM AUTHOR]

Application of EPR spectroscopy corroborated by spectra simulation in speciation studies of the tetravalent vanadium in supported VOx/ZrO2 catalyst has been discussed. Implementation of genetic algorithms into automated analysis of the EPR spectra has greatly improved the simulation efficiency. The performance of the new procedure has been benchmarked against common simplex method using the multi-component model and real EPR spectra of tetravalent vanadium in VOx/ZrO2 catalysts. The analysis has revealed speciation of vanadium into surface isolated and clustered vanadyl entities and isolated bulk VxZr ions due to formation of Zr1-x VxO2 solid solution in the near to surface region. The structural heterogeneity of vanadium can be controlled by the calcination temperature and the redox treatment. [ABSTRACT FROM AUTHOR]

A series of Nb-doped (0–23 wt%) cryptomelane catalyst (Nb-K-OMS-2) was synthesized and thoroughly characterized by XRD, TEM/EDX, XRF, XPS, XAS, UV-Vis, and Raman techniques corroborated by the work function measurements. The obtained catalysts were tested for soot oxidation (Printex U) in model tight and loose contact modes. It was shown that the catalytic properties of the Nb-K-OMS-2 are controlled by the amount of Nb dopant in a strongly non-monotonous way. The introduction of niobium gives rise to the strain in the cryptomelane lattice, accompanied by significant Mn+3/Mn+4 ratio variations and concomitant work function changes. The isotopic exchange experiments revealed that the catalytic activity of the Nb-OMS-2 catalysts in soot combustion proceeds via the pathways, where both the activated suprafacial 18O and the surface 16O2− species participate together in the reaction. The niobium doping level controls the non-monotonous changes of the catalyst work function and the lattice strain, and variations of these parameters correlate well with the observed deSoot activity. To our best knowledge, the role of the lattice strain of the cryptomelane catalysts was documented for the first time in this study. [ABSTRACT FROM AUTHOR]

Abstract: Vermiculite was treated with 0.8M solutions of hydrochloric and sulphuric acids for 2, 8, and 24h. The obtained materials were characterized with respect to their composition (XRF), structure (XRD, FTIR, UV–vis-DRS), texture (BET), surface acidity (NH3-TPD) and catalytic properties. Modification of vermiculite with acids significantly increased its surface area and pore volume and led to partial leaching of iron, aluminium and magnesium ions from its octahedral sheets. Efficiency of the leaching process depended on its duration and the nature of acid used. Acid treatment strongly modified the vermiculite structure leading to a distinct increase of its catalytic activity in the selective catalytic reduction of nitric oxide (SCR NO) process. In a series of the studied samples the best catalytic performance was found for vermiculite treated with sulphuric acid for 8h. [Copyright &y& Elsevier]

• Nanostructured Ce x Zr 1-x O 2 materials prepared by the continuous supercritical solvothermal sol-gel like synthesis. • Nanostructured Ce x Zr 1-x O 2 as supports of Ni impregnated dry reforming of methane (DRM) catalysts. • High TOF and small selectivity of coke formation in DRM. The nanostructured Ce x Zr 1-x O 2 systems (0 ≤ x ≤ 0.75) were prepared combining alkoxide and nitrate precursors in an ethanol/water mixture by the continuous supercritical solvothermal sol-gel like synthesis. They were subsequently used as supports for nickel impregnation (10 wt.%) to obtain catalysts for dry reforming of methane (DRM) reaction. A reference Ce x Zr 1-x O 2 (x = 0.50) system prepared via conventional coprecipitation method was used as a support for nickel impregnation in the comparative study of the nanostructured materials' catalytic potential. The morphological and structural properties of the prepared nanostructured supports and Ni-containing catalysts were investigated by numerous techniques as XRD, Raman spectroscopy, SEM, TEM, EDS, chemisorption and others. The conditions of DRM reaction were chosen in order to compare the activity, the stability as well as the selectivity of coke formation in the presence of the prepared catalytic materials. It was found that the industrial catalyst leads to heavy coking in the chosen conditions with a rapid loss of activity. While the nanostructured Ce x Zr 1-x O 2 (0 ≤ x ≤ 0.75) materials are found to be promising supports for Ni dispersion and coke control in DRM. In this study the nanostructured Ce 0.50 Zr 0.50 O 2 material impregnated with nickel shown the highest TOF and the smallest selectivity of coke formation in DRM among other nanostructured materials. The continuous supercritical solvothermal method allows to prepare nanostructured mixed oxide materials that could be promising supports for different active metals dispersion and for coke control in the reactions where coking may be abundant. [ABSTRACT FROM AUTHOR]