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Dry reforming of methane (DRM) is a promising way to convert methane and carbon dioxide into H

ChemCatChem 13(7), 1814 - 1823 (2021). doi:10.1002/cctc.202001829, We performed in‐situ XAS study of N$_{2}$O decomposition over CuO/CeO$_{2}$ catalysts. The Cu K‐edge and Ce L$_{3}$ ‐edge XANES and EXAFS analyses revealed the dynamic and crucial role of Cu$^{2+}$/Cu + and Ce$^{4+}$ /Ce$^{3+}$ ionic pairs during the catalytic reaction. We observed the initial formation of reduced Cu + and Ce$^{3+}$ species during activation in helium atmosphere at 400 °C, while concentration of these species decreased significantly during steady‐state nitrous oxide degradation reaction (2500 ppm N$_{2}$O in He at 400 °C). In‐situ EXAFS analysis further revealed a crucial role of copper‐ceria interface in this catalytic reaction. We observed dynamic changes in average number of Cu‐Ce scatters under reaction conditions, indicating an enlarging the interface between both copper and ceria phases, where electron and oxygen transfer occurs., Published by WILEY-VCH Verlag, Weinheim

Solution combustion synthesis was used to produce a junction between TiO2 and β-Bi2O3, which increases the photocatalytic activity of TiO2-β-Bi2O3 composites under visible and UV-light for the photocatalytic oxidation of aqueous Bisphenol A (BPA) solution. Surface (XPS, UV–vis DR analysis), electronic (EIS, EPR) and structural (SEM, TEM, XRD, N2 physisorption analysis) properties of the composites and BPA degradation performance were analyzed and correlated to the amount of β-Bi2O3 present in the composites (weight ratio Ti:Bi was varied between 1:0.2 and 1:0.8). The results show that (i) the narrow band gap semiconductor β-Bi2O3 acts as a visible-light photosensitizer for TiO2, (ii) a heterojunction between TiO2 and β-Bi2O3 enables the transfer of visible-light generated h+ from the valence band (VB) of β-Bi2O3 to the upper lying VB of TiO2, (iii) a p-n junction enables the transfer of visible-light photo-generated e− in the conduction band (CB) of β-Bi2O3 to the CB of TiO2, and (iv) under UV-light illumination both semiconductors act as scavengers for charge carriers generated by the other component. EPR measurements show that the amount of generated charge carriers and reactive oxygen species (ROS) was higher under UV-light illumination; besides, the amount of generated ROS increased with the increasing amount of β-Bi2O3 phase. On the other hand, BPA degradation runs and EIS measurements revealed that if the weight ratio Ti:Bi is over 1:0.4, the catalytic activity and the amount of generated charge carriers dropped due to excessive formation of a segregated β-Bi2O3 phase. The discrepancy between EPR measurements and catalytic BPA degradation tests can be contributed to the fact that BPA degradation proceeds either directly with photo-generated charge carriers (oxidizing organic species directly by photo-generated holes), or indirectly with ROS that include also EPR silent species (hydrogen peroxide and singlet oxygen).

The methane activation and methane dry reforming reactions were studied and compared over 4 wt % Ni/CeO2 and 4 wt % Ni/CeZrO2 (containing 20 wt % Zr) catalysts. Upon the incorporation of Zr into th...

CeO2, V2O5 and CeVO4 were synthesised as bulk oxides, or deposited over activated carbon, characterized by XRD, HRTEM, CO2-TPO, C3H8-TPR, DRIFTS and Raman techniques and tested in propane oxidative dehydrogenation using CO2. Complete oxidation of propane to CO and CO2 is favoured by lattice oxygen of CeO2. The temperature programmed experiments show the ~ 4 nm AC supported CeO2 crystallites become more susceptible to reduction by propane, but less prone to re-oxidation with CO2 compared to bulk CeO2. Catalytic activity of CeVO4/AC catalysts requires a 1–2 nm amorphous CeVO4 layer. During reaction, the amorphous CeVO4 layer crystallises and several atomic layers of carbon cover the CeVO4 surface, resulting in deactivation. During reaction, V2O5 is irreversibly reduced to V2O3. The lattice oxygen in bulk V2O5 favours catalytic activity and propene selectivity. Bulk V2O3 promotes only propane cracking with no propene selectivity. In VOx/AC materials, vanadium carbide is the catalytically active phase. Propane dehydrogenation over VC proceeds via chemisorbed oxygen species originating from the dissociated CO2. Graphic Abstract

Experimental and theoretical modeling on low-temperature dry methane reforming over Ni-containing CeO2 rods was studied. The catalyst was characterized by means of N2 physisorption, in-situ XRD, TPR and H2 chemisorption techniques. The characterization studies revealed the distortion of CeO2 flourite structure due to the Ni incorporation. Lattice expansion (due to reduction) and contraction (due to oxidation) suggest the reversible redox nature of CeO2. Ni–O–Ce solid solution formation was evidenced by both XRD and TPR studies. H2 chemisorption study revealed that the catalyst reduction temperature plays a significant role in Ni dispersion. The catalyst showed similar activity trends in two model geometries: a between-two-plates microchannel fixed-bed reactor and a conventional fixed-bed reactor. The activity tests were conducted in the kinetic regime, where conversions of CH4 were not influenced with the gas flow rate. A lattice Boltzmann model for mixed gas flow was developed along with a boundary condition for catalytic sites. The lattice Boltzmann model was used in a multiscale simulation of the studied reaction systems and produced data that qualitatively matched the experiments.

The effects of cobalt in the CeZrO2-supported NiCo (3 wt%, Co/ :Ni=3/2) on the DRM at 750oC were investigated by the transient method and use of 18O2 and 13CO2. Transient kinetic rates of carbon deposition and gasification by the support’s oxygen, TOF (s-1) and concentration of active carbon were determined. Higher TOF and reduced carbon accumulation rates were measured on NiCo than Ni at the initial stage of reaction. However, oxidation of Co with time-on-stream led to lower and higher concentration of active metal sites and deposited carbon, respectively. These results appear important for catalyst design improvements (e.g. metal alloy composition).

Propylene oxide (PO) is a versatile chemical, mainly used in the synthesis of polyurethane plastics. Propylene epoxidation using molecular oxygen could replace the tedious current synthesis protoco...

The course of the thermogravimetric degradation of LDPE in the presence of different aluminosilicate catalysts was modelled by applying a differential isoconversional Friedman approach. An analysis of catalyst-free PE-TG profiles confirmed that the degradation profiles predicted by various reaction models overlap over the entire conversion range once the data are analysed using a differential isoconversional Friedman approach. The results demonstrate that the catalytic degradation of LDPE can be predicted by a correlation twin, i.e. the two specific functional relations between the activation energy, pre-exponential factor and conversion. The crucial step for ensuring good agreement between the predicted and the measured profiles is to extrapolate the discrete values of the activation energies and pre-exponential factors to the zero conversion. It turns out that linear extrapolation and interpolation from the discrete values outperforms regression functions based on various order polynomials, and that apparent deviations from the global trend at lower conversions are not a consequence of the misinterpretation of the experimental results but are an experimental fact. The assumption about the compensation effect between the pre-exponential factor and activation energy holds within the conversion range from 10 to 90%. However, it is generally unsuitable for modelling purposes due to the uncertain extrapolation of the kinetic parameters to the zero conversion.

TiO2 nanorods (T) were combined with a narrow band gap semiconductor β-Bi2O3 (B) to form a heterojunction, which makes it possible for TiO2 to become active as a photocatalyst also under visible light illumination. To further increase the photocatalytic activity of TiO2 + Bi2O3/(BiO)2CO3 (TB) composite, we used a hydrothermal procedure to link it with reduced graphene oxide (rGO). Structural, surface and electronic properties of the obtained catalysts were analyzed and correlated to their performance in photocatalytic oxidation of aqueous bisphenol A (BPA) solution conducted in a batch reactor under visible light illumination. XRD, FTIR, UV–vis DR spectroscopy and photocurrent measurements of visible light illuminated TB composite catalyst clearly showed that (i) β-Bi2O3 acts as a photosensitizer for TiO2 and (BiO)2CO3 present in the TB composite, (ii) holes (h+) are photo-generated in valence band (VB) of β-Bi2O3 and due to the β-Bi2O3/TiO2 heterojunction transferred into VB of TiO2, (iii) p-n junction between β-Bi2O3 and TiO2 allows the photo-generated electrons (e−) in the conduction band (CB) of β-Bi2O3 to transfer to TiO2, and (iv) p-n junction between β-Bi2O3 and (BiO)2CO3 allows the photo-generated electrons in the conduction band of β-Bi2O3 to transfer to (BiO)2CO3. This means that more charge carriers are available to participate in the catalytic visible-light triggered oxidation process for the degradation of organic pollutants dissolved in water. The highest photocurrent density was measured for multi-phase TBR (TB + rGO) composite, which indicates that visible-light generated charge carriers in TB composite are injected into the reduced graphene oxide. The latter acts as a web for charge carrier percolation and suppresses the recombination of electron-hole pairs, thus resulting in improved catalytic activity of TBR. The results of UV–vis DR spectroscopy and photocurrent density measurements were entirely in line with the results of photocatalytic oxidation of water dissolved bisphenol A (BPA) in batch reactor under visible light illumination.

Amorphous TiO2 based nanotubes (TN) obtained through alkaline hydrothermal restructuring of P25 were treated with various acids and functionalized with hydrogen peroxide in order to tailor formation of structurally distinctive titanium peroxo species. Obtained solids were used as catalysts in the catalytic wet peroxide oxidation (CWPO) of model methyl orange (MO) aqueous solution under mild conditions. With the usage of 2 g/L of peroxide modified TN/ClO4p 0.01 catalyst and double stoichiometric amount of hydrogen peroxide, 50 ppm MO solution was purified up to 93% during 1 h at 40°C. No decay of catalyst activity was observed in 5 consecutive runs using the same catalyst batch. 17O NMR and TPD/MS analyses have revealed that catalytic activity of TN/ClO4p 0.01 sample can mainly be assigned to bidentate η2 surface peroxo species whose amount during 5 consecutive catalytic runs is almost constant, namely 5.9×10−7 and 5.2×10−7 mol/m2 prior and after usage, respectively. In addition, it has been observed that considerable amount of thermally labile oxygen species is used during 5 consecutive runs. From 17O NMR analysis we have observed that these species can be attributed to two coordinated (OTi2) oxygen formed on the place of terminal intra/interlayered −OH groups. Former can serve as structural stabilizing agents which enable formation of new η2 surface peroxo species during CWPO runs. To the best of our knowledge, this study is the first attempt to explain the possibility for η2 peroxo species structural stabilization during CWPO under mild conditions.

The effects of Ni particle size (dNi ∼ 22–45 nm) of Ni/Ce0.8Ti0.2O2-δ on the carbon paths in the dry reforming of methane at 750 °C have been investigated by various transient and isotopic experiments. The aim was to provide new insights for improving catalyst’s coke-resistance. Various correlations have been derived between dNi and (i) the initial kinetic rates (per Ni particle) of CH4 dissociation and CO disproportionation reactions along with their respective amounts of carbon accumulation, (ii) the integral rates of CH4 conversion and CO formation and the amount of carbon deposition in the DRM, and (iii) the rate of carbon removal by lattice oxygen of support compared to that by oxygen formed via the CO2 activation route during DRM. The former rate was found larger than the latter one independent of dNi (nm). CH4 dissociation is the exclusive route of inactive carbon formation during DRM independent of dNi.

Water-gas shift reaction (WGSR) and sorption enhanced water-gas shift reaction (SE-WGSR) were studied over Cu-zeolite 13X hybrid material (containing the catalyst and CO 2 sorbent) in the temperature range between 398 and 548 K. The copper phase was deposited by wet impregnation of binderless beads of 13X zeolite. The catalysts were characterized by N 2 sorption, XRD, He pycnometry and SEM-EDX techniques. In addition, the Cu-zeolite 13X hybrid material was also compared with a previously prepared and examined hybrid material, Cu-hydrotalcite hybrid material, used for the same purpose, the SE-WGSR.

Impregnation method was used to synthesize TiO 2 –WO 3 composites with two different TiO 2 morphologies (nanorods (R-TiO 2 –WO 3 ) and polyhedral nanoparticles (P-TiO 2 –WO 3 )). Their structural, morphological, surface properties and electron trapping states were analyzed and correlated to performance in photocatalytic bisphenol A oxidation. TiO 2 nanorods were prepared with alkaline hydrothermal digestion of commercially available high surface TiO 2 nanopowder (DT-51), which was used as a reference for TiO 2 nanoparticles. TEM analysis showed that in R-TiO 2 –WO 3 composites WO 3 is dispersed over the surface of TiO 2 nanorods in amorphous form and with increasing amount of WO 3 the TiO 2 crystal structure deteriorates. However, in the case of P-TiO 2 –WO 3 composite, multiphase system with monoclinic WO 3 intermixed with anatase TiO 2 was observed. Moreover, P-TiO 2 –WO 3 composite showed strong surface acidic sites, which were absent in R-TiO 2 –WO 3 composites; this information is significant to understand the depth of the electron trapping states. UV light-induced electron–hole pair excitations and decay dynamics in both TiO 2 –WO 3 composites were studied by infrared spectroscopy measurements and information about the conduction band (CB) electrons and surface trapping states of the composites were collected. In the case of composites with high density of shallow trapping states, enhanced photocatalytic activity was observed. On the contrary, lower photocatalytic activity of solids was observed in cases where deep trapping (TiO 2 nanoparticles) or fast recombination (R-TiO 2 –WO 3 composite) prevailed.

Syngas production from CH4 and CO2 was investigated over bimetallic nickel-cobalt catalysts, promoted by a CeZrO2 redox component. The appropriate design of active sites responsible for methane and CO2 activation (bimetallic clusters below 45 nm, adjacent to oxygen vacancy sites of the CeZrO2 solid solution) enabled kinetic balancing of both reaction halves, producing catalysts that are highly resistant to carbon accumulation in a wide range of CH4-CO2 feed compositions. With the employed approach, carbon accumulation can be prevented over metal clusters that are 2-fold larger compared to state-of-the-art. By anchoring the active NiCo bimetallic and CeZrO2 redox components over a high surface area β-SiC carrier (3NiCo/CeZrO2/S catalyst), the redox promoter is diluted and sintering of bimetallic NiCo clusters is reduced. At ambient pressure, a remarkably stable catalytic performance for 550 h was recorded with a produced H2/CO ratio of 0.82, methane reforming rate of 0.18 mol/gcat h and negligible carbon accumulation. Stable operation is maintained for 60 h during reforming at 20 bar, producing syngas with a H2/CO ratio of 0.33. Importantly, accumulated carbon yield is 2–3 orders of magnitude lower compared to state-of-the-art. These results constitute a promising basis for the design of a prospective technology for CO-rich syngas production through CH4-CO2 reforming.

Nickel (1.2 wt%) and cobalt (1.8 wt%) were dispersed over Ce0.75Zr0.25O2−δ solid solution (3NiCo EG) or over a mixture of CeO2 and ZrO2 single phases (3NiCo HT) and tested for dry reforming of methane (DRM) at 750 °C. The structural, morphological, textural and redox differences between 3NiCo EG and 3NiCo HT catalysts were probed by powder XRD, HAADF/STEM and SAED, N2 adsorption/desorption at 77 K, H2-chemisorption, H2-TPR and H2 transient isothermal reduction (H2-TIR) techniques. The origin, concentration and reactivity of “carbon” deposits formed in DRM (via the CH4 and CO2 activation routes) towards gaseous H2 and O2 but also towards the support's labile oxygen species in the prepared catalysts were analyzed by a series of various transient and SSITKA experiments (use of 18O2 and 13CO2). Regardless of the EG or HT support, the %-contribution of CH4 and CO2 to the “carbon” deposition is very similar but the amount and reactivity towards oxidation are largely different. On the other hand, the concentration of active carbon formed in the carbon pathway of the CO2 activation route is very small (θC < 0.16% after 2 h in DRM). Participation of mobile lattice oxygen species in gasification of deposited “carbon” to CO(g) does occur to a large extent on both EG- and HT-supported NiCo catalysts. The catalyst deactivation rate during the first 5 h of DRM was found to depend on the structure of the support (EG vs. HT). The faster deactivation observed with the 3NiCo EG catalyst cannot be linked to the existing differences in the rates of inactive “carbon” formation and depletion or the concentration of active carbon but rather to the different rates of encapsulation of NiCo bimetallic particles in the carbon layers formed (∼30 nm thick) as revealed by HAADF/STEM.

The as-synthesized TiO2 nanorods a-TNR (amorphous TiO2 layer covering the crystalline anatase TiO2 core) and TNR (fully crystalline anatase TiO2) were decorated with reduced graphene oxide (rGO) to synthesize two series of TiO2 + rGO composites with different nominal loadings of GO (from 4 to 20 wt%). The structural, surface and electronic properties of the obtained TiO2 + rGO composites were analyzed and correlated to their performance in the photocatalytic oxidation of aqueous bisphenol A solution. X-ray photoelectron spectroscopy (XPS) analyses revealed that charge separation in TiO2 + rGO composites is improved due to the perfect matching of TiO2 and rGO valence band maxima (VBM). Cyclic voltammetry (CV) experiments revealed that the peak-to-peak separations (ΔEp) are the lowest and the oxidation current densities are the highest for composites with a nominal 10 wt% GO content, meaning that it is much easier for the charge carriers to percolate through the solid, resulting in improved charge migration. Due to the high charge carrier mobility in rGO and perfect VBM matching between TiO2 and rGO, the electron–hole recombination in composites was suppressed, resulting in more electrons and holes being able to participate in the photocatalytic reaction. rGO amounts above 10 wt% decreased the photocatalytic activity; thus, it is critical to optimize its amount in the TiO2 + rGO composites for achieving the highest photocatalytic activity. BPA degradation rates correlated completely with the results of the CV measurements, which directly evidenced improved charge separation and migration as the crucial parameters governing photocatalysis.

In this work, a combination of ex situ (STEM-EELS, STEM-EDX, H2-TPR and XPS), in situ (CO-DRIFTS) and operando (DR UV–vis and DRIFTS) approaches was used to probe the active sites and determine the mechanism of N2O decomposition over highly active 4 wt.% Cu/CeO2 catalyst. In addition, reaction pathways of catalyst deactivation in the presence of NO and H2O were identified. The results of operando DR UV–vis spectroscopic tests suggest that [Cu−O−Cu]2+ sites play a crucial role in catalytic N2O decomposition pathway. Due to exposure of {1 0 0} and {1 1 0} high-energy surface planes, nanorod-shaped CeO2 support simultaneously exhibits enhancement of CuO/CeO2 redox properties through the presence of Ce3+/Ce4+ redox pair. Its dominant role of binuclear Cu+ site regeneration through the recombination and desorption of molecular oxygen is accompanied by its minor active participation in direct N2O decomposition. NO and H2O have completely different inhibiting action on the N2O decomposition reaction. Water molecules strongly and dissociatively bind to oxygen vacancy sites of CeO2 and block further oxygen transfer as well as regeneration of catalyst active sites. On the other hand, the effect of NO is expressed through competitive oxidation to NO2, which consumes labile oxygen from CeO2 and decelerates [Cu+ Cu+] active site regeneration.

Catalytic depolymerization of polyethylene (PE) over several aluminosilicate catalysts was studied using thermogravimetric (TG) analysis. Procedure was proposed for decoupling mass loss related directly to the catalyst and that of PE depolymerization. The benefit of this approach is twofold: (1) It enables a more realistic kinetic analysis, and (2) reduces the total number of required experiments with the pure catalyst by more than 50 %. The activation energies of PE depolymerization over different catalysts were calculated from the treated PE-TG profiles using advanced isoconversional analysis and were compared to those obtained from raw TG profiles. The presented analysis reveals that neglecting the mass loss associated with the aluminosilicate catalyst results in underestimated values of calculated activation energies at low PE conversions, while at high conversions the values of calculated activation energies were overestimated. The apparent PE depolymerization activation energy in the presence of applied catalysts increases in the following order: amorphous silica alumina

Water-gas shift reaction and sorption enhanced water-gas shift were studied over Cu-CeO2 and Cu-HTlc catalysts in the temperature range between 125 and 295 °C. The catalysts were characterized by N2 sorption, XRD, H2-TPR and SEM techniques. Among the tested catalysts, copper supported on polyhedral ceria nanoparticles showed the highest activity, achieving 87.6% CO conversion. High dispersion of copper was identified as a catalyst property required for high WGS activity. During SE-WGS tests using either a multilayer arrangement of Cu-CeO2 catalyst and K-HTlc sorbent, or Cu promoted hydrotalcite hybrid catalyst, nearly 70 mol% H2 was obtained in the product gas stream during the initial transient period. Elevated pressure and surplus of steam in the feed increased the sorption capacity of K-HTlc, resulting in delayed CO2 breakthrough. On the other hand, dilution of feed stream with inert gas (He) resulted in a dramatic decrease of sorbent’s capacity leading to an early CO2 breakthrough.

This research focuses on epoxidation of propylene over pristine, Na, Ca and Cs modified CuOx/SiO2 catalysts using O2. The selectivity of the reaction is analyzed using a combination of catalytic tests, in-situ XAS and DFT calculations. The initially present subnanometer CuO clusters are present in all catalysts which re-disperse/flatten during reaction. During catalytic reaction, the Cu1+ becomes the predominant oxidation state. There is no correlation between propylene oxide (PO) selectivity and copper oxidation state. DFT analysis of the propylene reaction pathway revealed that Na, Cs, and Ca addition decreases the bonding strength of propylene to CuO and decreases the O2 activation barrier, while simultaneously increase the exothermicity of O2 dissociation. The Na induced Cu–O bond modification decreases the activation barrier from 0.87 to 0.71 eV for the oxametallacycle (OMC) ring closure (first step in the reaction pathway favoring selectivity towards PO) compared to pristine 5Cu catalyst. At the same time, we observed an increase (from 0.45 to 0.72 eV) of the barrier for the abstraction of allylic hydrogen. The opposite effect is achieved by Ca addition: the activation barrier for OMC ring closure increases to 1.08 eV and that for allylic hydrogen stripping decreases to 0.16 eV.

The gas-phase conversion of glycerol into allyl alcohol over Fe–Mo and Cs–Fe–Mo/HZSM-5 (with SiO2/Al2O3 = 30 and 1500) zeolite catalysts in a packed-bed continuous flow reactor has been reported for the first time. To the best of our knowledge, the Cs–Fe–Mo/HZSM-5 catalyst appears to be most promising for gas-phase conversion of glycerol into allyl alcohol. The structure and catalytic performance for the glycerol conversion over bi- and tri-metallic-promoted zeolite catalysts were studied. The synthesized catalysts were characterized by ICP–AES, ICP–MS, N2 physisorption, SEM, STEM–EDX, XRD, NH3–TPD, CO2–TPD, XPS, TGA and pyridine-DRIFT techniques, which showed that differences in catalysts activity and product distribution are influenced by metal loading, changes of acid-base, and porosity. The most stable allyl alcohol selectivity achieved was 46.1 mol.% at 98.1 mol.% glycerol conversion over the 5wt.%Cs–2.5wt.%Fe–2.5wt.%Mo/HZSM-5 (SiO2/Al2O3 = 1500) catalyst achieved with 10 wt% glycerol feed at 350 °C reaction temperature after 26 h time-on-stream. The superior performance of the synthesized catalyst was attributed to the presence of the basic sites, high mesopore volume and mesopore surface area, balance between acidic-basic sites, synergetic interaction between metal species and ZSM-5 zeolite support. The reaction pathway mechanisms of glycerol to value-added allyl alcohol via the direct glycerol dehydration and hydrogen transfer mechanism over basic sites are proposed.

In this work we report the pioneering gas-phase conversion of glycerol into glycidol in one-step over Cs–ZSM-5 zeolite catalyst with SiO2/Al2O3 = 1500. The structure and catalytic performance of catalysts synthesized by wet impregnation method with different Cs loadings were studied. The catalysts were characterized by ICP–MS, XRD, N2 physisorption, STEM–EDX, SEM, pyridine-DRIFT, CO2–TPD, NH3–TPD, and TGA techniques. The reaction was carried out in a packed-bed continuous flow reactor under atmospheric pressure. The highest achieved glycidol yield was 40.4 mol% over 20 wt% Cs–ZSM-5(1500) catalyst with 10 wt% glycerol in the feed at 350 °C reaction temperature and GHSVtotal = 1250 h−1. The glycidol selectivity was increasing steadily from 41.4 to 64.3 mol% during 27 h time-on-stream. This catalyst showed relatively high stability and selectivity, which was attributed to the presence of a suitable amount of basic sites and the strong CsNO3/HZSM-5 support synergetic interaction. Based on the identified reaction products, we propose the reaction mechanism of the catalytic glycerol conversion to glycidol over the tested catalysts. It was revealed by SEM and XRD that Si species partly dissolved from HZSM-5 framework after impregnation with CsNO3. Furthermore, we showed that the catalyst deactivation depends on the amount of CsNO3 active phase (basic sites) and the coke formation. The catalytic results demonstrate that at the beginning the glycerol conversion dropped down when CsNO3 was partly decomposed during the reaction, while the second deactivation stage with a slow decrease of catalyst performance corresponded to the coke formation.

Monometallic (CuO and FeOx) and bimetallic (CuFeOx) entities on different supports are promising transition-metal low-cost catalysts for catalytic oxidation of volatile organic compounds (VOC) from industrial air alternatively to noble-metal catalysts which are currently in use. In this work we report for the first time that the promotion of catalytic oxidation of toluene as a model VOC is due to the cooperative redox effect between CuO nanocrystals and finely dispersed Cu-oxo-Fe clusters on mesoporous silica with defined Fe/Cu molar ratio. This increases the number and reactivity of adsorbed electrophilic (O− and O2−) as well as nucleophilic lattice oxygen (O2-) species at the CuO crystal and and Cu-oxo-Fe cluster interface, thus providing up to twofold enhancement in catalytic activity for total oxidation of toluene. Catalysts were prepared via direct synthesis of Fe-functionalized disordered mesoporous silica containing only isolated iron sites followed by copper addition via impregnation.

CoFe, CoW, NiFe and NiW bimetallic pairs deposited over CeO2–ZrO2 promoted ordered mesoporous γ-Al2O3 were tested in the methane dry reforming reaction. The catalysts were characterized by N2 adsorption, wide and small angle XRD, TEM, UV-vis DRS and H2-TPR techniques. Upon thermal treatment, diffusion of Ni and Co into the alumina matrix occurred, resulting in the formation of corresponding aluminate spinels. Based on UV-vis characterization, the formation of bulk Fe2O3 could be only tentatively assigned to the NiFe/AlCZ catalyst. Bulk Co3O4 is likely present in both CoW and CoFe catalysts. CoFe/AlCZ and NiFe/AlCZ catalysts achieved high and stable methane conversion rates of 8.8 and 6.0 mmol of CH4 per gcat per min, respectively. The activity of tungsten-containing catalysts (CoW/AlCZ and NiW/AlCZ) was substantially lower compared to iron-containing catalysts (2.8 and 0.8 mmol of CH4 per gcat per min, respectively) and their deactivation was likely related to sintering and oxidation of active metal clusters. A low carbon content was accumulated on the surface of spent NiFe/AlCZ, CoFe/AlCZ and NiW/AlCZ catalysts after 20 h tests (0.6–1.2 wt%), indicating the high efficiency of the redox promoter under dry reforming conditions.

Different chemical modifications were performed to the natural aluminosilicate Montanit300® in order to improve its catalytic activity in PE depolymerization. Performance of such prepared catalysts was compared to established solid acid catalysts, such as HZSM-5, sulfonated and fluorinated γ-Al2O3 and amorphous silica–alumina. Pyridine TG and DRIFTS characterization revealed mild acid treatment and aluminum grafting as successful in increasing acid site density through impurity removal and specific surface area increase. Mesoporous catalyst structure that allows facile diffusion through its pore network, together with high-density Bronsted acid sites, was found to be crucial to obtain high catalytic activity. The T50 value for PE depolymerization was lowered by 162 °C with sulfonated γ-Al2O3 solid, compared to non-catalyzed reaction, whereas with aluminum-grafted Montanit300® catalyst this value was lowered by 65 °C. PE depolymerization products present in the condensed liquid phase using aluminum-grafted Montanit300® catalyst were exclusively alkanes with chain length up to 21 carbon atoms. Liquid, coke and gas yields were found to be 53, 0.4 and 46.6%, respectively, the latter consisting of linear and branched C2–C4 alkenes and alkanes.

This study reports a thorough investigation of nanosized CuO/CeO2 materials as an efficient catalyst for decomposition of N2O, which is a strong greenhouse gas largely produced by chemical industry. Effect of terminating CeO2 crystalline planes ({100}, {110}, and {111}) on the behavior of CuO dispersed over CeO2 nanocubes, nanorods and polyhedral crystallites was examined in detail by using a variety of catalyst characterization techniques. The 4 wt % Cu was found as the most advantageous metal loading, whereas higher Cu content resulted in lower dispersion and formation of significantly less active, segregated bulk CuO phase. It was discovered that CuO/CeO2 solids should enable both excessive oxygen mobility on the catalyst surface as well as formation of highly reducible Cu defect sites, in order to ensure high intrinsic activity. Detailed studies further revealed that CeO2 morphology needs to be tailored to expose {100} and {110} high-energy surface planes, as present in CeO2 nanorods. Oxygen mobility ...

This study explores CeZrO2 deposited over commercial β-SiC, and a highly ordered 3D β-SiC synthesised in the laboratory via electrophoretic deposition, as well as γ-Al2O3 in order to prepare three types of dual support for NiCo bimetallic catalyst in CH4–CO2 dry reforming (DR). CeZrO2 was deposited over γ-Al2O3 and β-SiC by dry impregnation (DI), wet impregnation (WI) and 2-step deposition precipitation (DP). XRD analysis indicated that the constituents of the dual supports were retained after calcination, as well as before and after the DR reaction. CeZrO2 remained as a mixed oxide solid solution, whilst alumina formed spinel structures with Ni and Co before the catalysts were reduced in H2 during the pretreatment step prior to the activity tests. During 550 h stability tests, WI, 2-step SICAT/CeZrO2 and 2-step γ-Al2O3/CeZrO2 solids were identified as the most promising catalysts, maintaining high DR activities without deactivation. Notably, 2-step SiC(SICAT) and 2-step γ-Al2O3/CeZrO2 samples recorded the highest yield (H2 = 77%, CO = 90%; H2 = 71%, CO = 81%), with a coke content of 7.7 and 0.6 wt.%, respectively. Carbon deposition for the former is high; contrarily, for WI SiC(SICAT) solid, it accumulated a lower amount of 2.6 wt.%. No agglomeration of CeZrO2 and NiCo phases was observed, evidencing excellent robustness and thermal resistance of these dual supports.

Mesoporous zirconia and nickel incorporated zirconia catalysts were prepared following different routes. Synthesis of mesoporous zirconia and Ni incorporated zirconia with very narrow pore size distributions and high surface area was achieved. Ni incorporated mesoporous zirconia materials showed high activity in carbon dioxide reforming of methane, performed at 600 degrees C. Coke formation during dry reforming was eliminated over the Ni incorporated zirconia catalyst prepared by the one-pot procedure, using Pluronic P123 as the surfactant. It was shown that Ni was very well distributed within this material with cluster sizes smaller than the detection limit of XRD. This catalyst also showed highly stable catalytic performance. However, the catalysts prepared by the impregnation method showed higher activity but much higher coke formation than the catalyst prepared by the one-pot route. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

In this work, CuOx/SiO2 catalysts were investigated in the propylene partial oxidation reaction. Ordered mesoporous silica (KIT-6) was used to deposit 1–10 wt. % copper and subsequently modified with Na, K and Ca. The synthesized materials were characterized by N2 physisorption, XRD, TEM-EDS, CO2-TPD, operando UV/Vis DRS, operando XANES and pyridine DRIFT spectroscopy. Regardless of the CuOx loading, catalyst deactivation was observed during propylene oxidation reaction in non-modified catalysts, which was related to sintering of oligomeric [Cu-O-Cu]n species. Sintering of CuOx is strongly promoted under a reducing propylene atmosphere and related to the presence of Cu+1. The resulting bulk CuOx promotes acrolein selectivity. We produced modified catalysts with finely dispersed alkali metal cations, associated with the subnanometer CuOx phase, resulting in a greatly stabilized morphology and catalytic activity. Operando XANES analysis revealed that a substantial fraction of Cu2+ is transformed to Cu+ during the propylene oxidation reaction (52–68%, depending on the modifying atom). Also, the dynamics of reaching the quasi steady oxidation state differ strongly. The kinetics of oxygen abstraction and replenishment are substantially different, indicative of modified chemistry of the nucleophilic oxygen species, present in 5CuNa catalyst in contrast to others (5Cu and 5CuCa). We propose that Cu+ is not crucial for PO formation. Instead the electropositive Na+ and K+ decrease the nucleophilic strength of oxygen in CuOx, by attracting its electrons. Consequently, the catalytic action of oxygen changes from oxidative attack on the allylic hydrogen to oxygen insertion into the C C bond of propylene. This results in a noticeable selectivity shift from acrolein to propylene oxide. The effect of calcium on decreasing the nucleophilic character of O species in CuOx is negated by charge compensation by strongly adsorbed hydroxyl groups and Ca modification for PO selectivity is inefficient. Additionally we found, that further oxidation of propylene oxide is, most likely, the main factor determining high selectivity for COx products. The alkali modification which increases the PO selectivity does not function via elimination of LAS, but exclusively through attenuation of nucleophilic character of oxygen species.

High surface area CeO 2 nanospheres as an active catalyst support were synthesized using glycothermal approach. Different loadings of copper (4, 6, 10 and 15 wt.%) were supported by wet impregnation method. Prepared materials were characterized by means of TEM, SEM-EDX, XRD, UV-Vis diffuse reflectance, N 2 adsorption/desorption, DRIFT and H 2 -TPR techniques, and tested for the catalytic reaction of nitrous oxide decomposition. The best activity in the N 2 O degradation was found for the sample containing 10 wt.% of Cu that can be attributed to the highest number of small CuO clusters on the catalyst surface. Further increase of copper content strongly affects the dispersion and leads to the formation of less active segregated CuO phase, which was confirmed by XRD, UV-Vis and H 2 -TPR results. Accordingly to UV–Vis examination and DRIFT analysis using CO as a probe molecule, all solids contain Cu +1 ions which play a crucial role in the N 2 O decomposition mechanism. The synthesized catalysts were also tested in wet or NO containing atmospheres, where an inhibiting effect takes place and leads to shifting of conversion profiles to higher temperature by 65 and 10 °C, correspondingly. It was found out that the formation of a new, crystalline CuO·3H 2 O phase occurs in water vapour containing atmosphere, which can result in catalyst deactivation. However, this effect is fully reversible and the catalyst is able to replenish initial activity in dry atmosphere. Potentiality of CuO/CeO 2 materials in catalytic N 2 O decomposition in industrial processes was confirmed by long-term stability tests performed in the period of 50 h in the presence of inhibiting gas components.

The effect of nanomaterials on biota under realistic environmental conditions is an important question. However, there is still a lack of knowledge on how different illumination conditions alter the toxicity of some photocatalytic nanomaterials. We have investigated how environmentally relevant UV-A exposure (intensity 8.50 ± 0.61 W/m 2 , exposure dose 9.0 J/cm 2 ) affected the toxicity of cerium oxide (CeO 2 )-based nanostructured materials to the early-life stages of zebrafish Danio rerio . Pure cerium oxide (CeO 2 ), copper–cerium (CuO–CeO 2 ) (with a nominal 10, 15 and 20 mol.% CuO content), cerium–zirconium (CeO 2 –ZrO 2 ) and nickel and cobalt (Ni–Co) deposited over CeO 2 –ZrO 2 were tested. It was found that under both illumination regimes, none of the tested materials affected the normal development or induced mortality of zebrafish early-life stages up to 100 mg/L. Only in the case of CuO–CeO 2 , the growth of larvae was decreased (96 h LOEC values for CuCe10, CuCe15 and CuCe20 were 50, 50 and 10 mg/L, respectively). To conclude, CeO 2 -based nanostructured materials are not severely toxic to zebrafish and environmentally relevant UV-A exposure does not enhance their toxicity.

Catalytic decarboxylation is a novel and promising pathway for continuous and efficient conversion of organic wastewaters. Stable conversion of acetic acid to CH4 and CO2 mixtures (T ≥ 225 °C, Sp > 80%, 70 h TOS) was demonstrated. Approaches for overcoming catalyst deactivation during production of H2-rich gas from formic acid are outlined.

This study assesses the impact of different support materials (Mutag BioChip™, expanded clay and activated carbon) on microbial hydrogen production in an anaerobic packed-bed reactor (APBR) treating synthetic waste water containing glucose as the main carbon source at low pH value. The APBRs were inoculated with acid pretreated anaerobic sludge and operated at pH value of 4±0.2 and hydraulic retention time (HRT) of 3h. The maximum hydrogen yield of 1.80mol H2/mol glucose was achieved for the APBR packed with Mutag BioChip™ (R1), followed by expanded clay (R2, 1.74mol H2/mol glucose) and activated carbon (R3, 1.46mol H2/mol glucose). It was observed that the investigated support materials influenced the immobilization of hydrogen producing bacteria and consequently hydrogen production performance as well as composition of soluble metabolites. The main metabolic products were acetic acid and butyric acid accompanied with a smaller content of ethanol. The data indicated that in reactors with higher hydrogen yield (R1 and R2), acetate/butyrate (HAc/HBu) ratios were 1.7 and 1.6, respectively, while in the reactor with the lowest hydrogen yield (R3) the obtained HAc/HBu ratio was 4.8. Finally, stable hydrogen and organic acids production throughout the steady-state operation period at low pH values was achieved in all reactors.

The as-synthesized TiO

Complex waste streams originating from extraction processes containing residual organic solvents and increased C/N ratios have not yet been considered as feedstock for biogas production to a great extent. In this study, spent rosehip (Rosa canina L.) solid residue (64% VS, 22 MJ/kg HHV, 30C/1N) was obtained from an industrial ethanol aided extraction process, and extensively examined in an automated batch bioreactor system for biogas production. Fraction separation of the compact lignocellulosic seeds increased the available sugar and ethanol content, resulting in high biogas potential of the sieved residue (516 NL/kg VS’). In co-digestion of spent rosehip substrate with non-deactivated nitrogen rich microbial co-substrates, methanogenesis was favored ( Y m > 68 % CH 4 ). In individual digestion of microbial co-substrates, this was not the case, as biogas with 28 vol.% N2 was produced from activated sludge supplement. Therefore, effective inhibition of exogenous microbiota was achieved in the presence of carbonaceous spent rose hip.

Ordered mesoporous CuO–CeO2 mixed oxides with different Cu loadings were synthesized by means of hard template replication approach using mesoporous silica KIT-6 as a template. Prepared materials were characterized by SEM-EDX, XRD, UV–Vis DR, N2 adsorption/desorption, and H2-TPR techniques. The catalytic decomposition of N2O was studied in a fixed-bed reactor in the temperature range from 300 °C to 600 °C and GHSV = 45,000 h−1. Solids prepared by replication approach showed superior catalytic activity in comparison to materials synthesized by conventional preparation methods. Among the solids tested, the highest conversion of N2O was observed in the presence of a catalyst containing 40 mol.% Cu. Reduction of prepared samples occurs at much lower temperatures in comparison to individual CuO and CeO2 oxides due to synergetic effect present in mixed oxides. N2O decomposition tests revealed very good agreement between the catalytic activity and material reducibility, which increased with increasing Cu content from 25 to 40 mol.%. Formation of segregated CuO phase was observed for samples with Cu content above 40 mol.%. Accordingly to UV–Vis examination, all solids contain Cu+1 and Ce+3, which play a crucial role in the N2O decomposition mechanism. In wet (1.5 vol.% H2O) or NO (1.5 vol.%) containing atmospheres, where inhibiting effect due to competitive adsorption of water and NO molecules on active sites takes place, resulting conversion profiles were shifted to higher temperature by 70 °C and 25 °C, respectively. Results of long-term stability test performed in the period of 50 h confirmed good catalytic stability of an investigated material, which can be attributed to catalyst ability to regenerate active sites by desorption of formed oxygen from the catalyst surface.

To improve the activity of nickel–cobalt (NiCo) catalyst supported on ceria-zirconia (CeZr) in the dry reforming of methane (DRM) with carbon dioxide, and to lower the coking rate in this process, 1.5 wt.% and 2.5 wt.% NiCo catalysts were prepared using two approaches, i.e. freeze-drying (FD) and NO calcination for comparison against oven-drying (OD) and air calcination (air), respectively. Their impact was studied for 20 h of DRM at 750 °C and 1.2 bar, with undiluted CH4–CO2 feed simulating the real conditions. NO-calcined samples show, on average, more pronounced improvement through increased conversion of CH4 (90%), followed by FD samples (85%) from the air and OD-prepared samples (both 82%). Coking content varied between 0.67 and 0.82 wt.%. The observed slow catalyst deactivation might be caused by sintering of the catalysts. Higher quantity of CO than H2 for syngas production was obtained, owing to concurrent reverse water-gas shift side reaction, and high redox properties of the defective CeZr lattice that enabled surface carbon gasification by continuous replenishment of oxygen from the support to produce CO, of which the latter phenomenon also explains the low carbon deposition. H2/CO ratio between 0.42 and 0.85 was achieved, with FD and NO samples fared better (0.83–0.85) over the ones prepared by conventional methods (0.73–0.82) for 2.5%NiCo loaded catalysts.

Ceria zirconia solid solution with a high specific surface area and oxygen storage capacity was used to support NiCo bimetallic nanoparticles and was successfully employed as a catalyst in the methane–CO2 reforming reaction. During the reforming test with an equimolar CH4/CO2 ratio at 1023 K, an initial catalyst deactivation was observed, which was followed by a slow self-reactivation. The catalyst reached its initial activity after approximately 400 h TOS with negligible carbon accumulation and H2 and CO yields of 71 and 85 %, respectively. Catalyst deactivation in the initial 25 h of reaction could be correlated to the oxidation of nanosized NiCo particles by water produced through the reversed water gas shift reaction pathway. With prolonged time on stream, sintering and growth of nanosized NiCo particles occurs, which makes them less susceptible to oxidation and slowly leads to their reduction and reactivation. In parallel, recrystallization of Ce0.8Zr0.2O2 support from cubic crystallites to a more irregular polyhedral shape occurs, which improves the oxygen storage capacity of the material and significantly contributes to the catalyst regeneration. The rate of catalyst regeneration mainly depends on the rate of Ce0.8Zr0.2O2 support recrystallization, which is driven by sintering, and is consequently much slower than the initial deactivation. Upon increasing the CH4/CO2 feed ratio to 1.5 and 2.33, water yields were significantly reduced and the previously observed catalyst deactivation could be strongly decreased or even completely avoided.

It is important to understand each analytical system and its limitations when performing any chromatographic measurements. In the present paper, a methodology for method validation and measurement uncertainty evaluation for the measurement of volume fractions of selected gases (CO2, CO, CH4, H2) in simulated reformate gas streams by using gas chromatography was developed. A detailed procedure for in-house method validation based on a simple experimental design and consistent statistics is presented. The analytical protocol allowed us to quantify gases in volume fractions from 2.00 to 100.0 mL/(100 mL) with satisfactory recoveries. We proved that the method was selective for the measurement of gases in simulated reformate gas stream. In addition, a step-by-step illustration of modelling approach for measurement uncertainty evaluation of each component is also provided. Uncertainty arising from repeatability and trueness is relatively low, while the contribution from reproducibility is of higher level for all the analytes tested. The main reason for this is changes in atmospheric pressure that affect gas chromatographic measurements. Solution of this problem could be more frequent calibration of apparatus, yielding to higher costs and more time-consuming process, or by measuring the atmospheric pressure and using it to correct the response of the gas chromatograph for resulting variations in sample size. The obtained results confirm that it is imperative to fully characterize the analytical system before proceeding with an analysis.

Titanate nanotube-based catalysts were prepared via alkaline hydrothermal synthesis route followed by heat-treatment at different temperatures, ranging from 300 to 700 °C. The resulting metal-free solids were then applied as a catalyst in a three-phase trickle-bed reactor, where catalytic wet air oxidation (CWAO) reactions of model aqueous bisphenol A (BPA) solution were performed. Mainly, the CWAO experiments were conducted at 200 °C with oxygen partial pressure of 10 bar over 300 mg of a catalyst. It was observed in the given range of operating conditions that BPA undergoes both non-catalytic as well as catalytic oxidation routes, while the latter is far more pronounced. At 210 °C and in the presence of 0.5 g of titanate nanotube-based catalyst, which was annealed at 600 °C, complete BPA removal was obtained. From TOC point of view, approximately 70% conversion was achieved indicating the persistence of refractory intermediates of lower carboxylic acids. The cross-section of results derived from various analytical techniques, which were used to identify surface, textural and morphological properties, revealed that balanced physicochemical properties are required to achieve meaningful extent of BPA removal. During 2–4 day time on stream, no catalyst deactivation occurred that could be attributed to the dissolution of active powders, or to the carbonaceous deposits accumulated on the catalyst surface. Therefore, these nanotubular materials can be regarded as innocuous and efficient long-term catalysts for oxidation of hazardous organic compounds (such as BPA) in the CWAO process.

High surface area CeO 2 –ZrO 2 (80/20 wt.%) mixed oxide supports with superior reducibility were synthesized by two solvothermal approaches, hydrothermal aging in NH 4 OH aqueous solution and glycothermal aging in ethylene glycol. The materials aged in alkaline water at elevated temperature and pressure exhibit large crystallite sizes (roughly 30–40 nm), and structural segregation of the CeO 2 and ZrO 2 crystal phases. The materials synthesized by reduction in ethylene glycol show properties of homogeneous solid solutions with highly developed nanocrystalline structure (an average crystallite size was estimated at about 6 nm). Bare CeO 2 –ZrO 2 supports were selected mostly on grounds of their reducibility for the subsequent homogeneous deposition coprecipitation with nickel and cobalt (3, 6, 12, 18 wt.%) loadings. The bimetallic catalysts were thoroughly characterized and then examined in the catalytic CO 2 –CH 4 reforming reaction. The materials which exhibited both small crystallite sizes of the employed support and small active bimetallic particles, demonstrated high catalytic activity and good resistance to carbon accumulation on the catalyst surface. Dry reforming process over catalysts bearing glycothermally aged supports revealed the simultaneous occurrence of reverse water gas shift reaction, whereas the hydrothermally prepared supports stimulate methane dehydrogenation reaction at higher temperatures; the occurrence of both reactions is influenced by the dispersion of active metal species.

Two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2–ZrO2 mixed oxides on a 80–20 wt.% basis. Aging parameters, such as time and temperature, were systematically investigated in order to determine the optimal conditions to maintain high surface area and oxygen mobility of the prepared solids. Different loadings of nickel and cobalt (3, 6, 12 and 18 wt.%) were subsequently deposited via homogeneous deposition precipitation method. Calcined bimetallic catalysts were characterized by N2 adsorption–desorption, XRD, H2-TPR, TPO-TGA and FE-SEM methods, and tested for activity, selectivity and stability in the reforming of equimolar CH4–CO2 gas streams. During temperature programmed methane reforming tests, syngas with a H2/CO ratio between 0.3 and 0.79 was produced. Growth of carbon nanofilaments over the catalyst does not lead to deactivation, but can cause reactor plugging. Two conditions are vital and must be fulfilled simultaneously to avoid excessive carbon deposition: strong interaction between the NiCo bimetallic particles and CeZr support, which exists only at NiCo loadings up to 6 wt.%, as well as high oxygen mobility within the highly defective CeO2–ZrO2 crystalline lattice for timely carbon oxidation.

Effects of four different nanocrystalline CeO 2 -based catalysts on crustaceans Daphnia magna and early-life stages of zebrafish Danio rerio were studied. Pure CeO 2 and CuO–CeO 2 mixed oxides with a nominal 10, 15 and 20 mol.% CuO content were tested. Pure CeO 2 provoked no effects, but CuO–CeO 2 mixed oxides induced some sublethal effects on fish and affected daphnids’ survival. The most pronounced effects were found on fish body growth, which was reduced at 10 mg/L in case of CuCe20 and 50 mg/L in cases of CuCe10 and CuCe15. Daphnids’ survival was affected above 80 mg/L of CuCe20, while CuCe10 and CuCe15 did not affect daphnids. None of the materials was highly toxic to daphnids and fish in comparison to some other environmental pollutants. Differences in effects between the materials could not be explained by their specific physicochemical properties. This work indicates that more attention should be placed at potential toxicity of nanostructured materials, such as nanocrystalline mixed-oxides.