Catalytic behaviour of transition metal carbides of group 5 in the methanol steam reforming

Transition metal carbides of group 5 (G5TMC=VC, NbC and TaC) with similar crystallite sizes were prepared by a sol-gel route. The catalysts were characterized and studied in the methanol steam reforming (MSR) reaction in the temperature range of 573–723 K at atmospheric pressure and using a stoichiometric CH3OH/H2O = 1/1 mole ratio mixture. Under the MSR reaction conditions used, the route of methanol transformation depends on the G5TMC used as catalyst. The catalytic behaviour of VC differs from that of NbC and TaC, which in turn show a similar behaviour. Over VC, methanol is mainly converted to a mixture of H2+CH4, whereas over NbC and TaC the major product obtained is HCHO, formed from the dehydrogenation of methanol

Insights into the use of Flash Sintering methods to prepare catalytic materials

Please click Additional Files below to see the full abstract

An in-situ DRIFTS-MS study of the photocatalytic H2 production from ethanol(aq) vapor over Pt/TiO2 and Pt-Ga/TiO2 catalysts

In this paper, Pt/TiO2 and Ptsingle bondGa/TiO2 catalysts with similar Pt dispersion and similar structural and morphological characteristics were compared in the H2 production from the phototransformation of aqueous solutions of ethanol. Catalysts were characterized by means of N2 adsorption-desorption, XRD, Raman, H2-TPR, UV–Vis diffuse reflectance spectroscopy, XPS and CO chemisorption. The photocatalytic reaction was carried out in liquid and vapour phase. The photocatalytic transformation of ethanol(aq) vapour over Pt/TiO2 and Ptsingle bondGa/TiO2 catalysts was studied by in situ DRIFTS-MS. Differences in the photocatalytic transformation of ethanol(aq) over Pt/TiO2 and Ptsingle bondGa/TiO2 were determined. The effect of Ga is analysed in the light of the evolution of surface species under photocatalytic reaction conditions

CO2 reduction over Cu-ZnGaMO (M = Al, Zr) catalysts prepared by a sol-gel method: Unique performance for the RWGS reaction

Cu-ZnGaMO (M = Al, Zr) catalysts prepared by a surfactant-free sol-gel method were characterized and tested in the reverse water-gas shift (RWGS) reaction. Their catalytic behavior was analyzed under 0.1–3 MPa at 250–325 °C and using a reactant mixture of CO2/H2 = 1/3. The catalytic results are analyzed in the light of the characteristics of the catalysts. The Cu-ZnGaZrO catalysts were highly selective for the RWGS reaction; a major role of surface copper and interface oxygen vacancies is proposed. CO2 conversion and CO selectivity increased on increasing the reaction temperature. CO2 conversion reaches 16.8% with 99.7% selectivity for CO under 0.1 MPa at 325 °C over the Cu-ZnGaZrO1 catalyst. It is suggested that CO and methanol production proceed via independent reaction pathways

Preparation and characterization of bulk Mo⁠xC catalysts and their use in the reverse water-gas shift reaction

In this work, different routes for the preparation of molybdenum carbides through sol-gel methods were studied; several parameters such as molybdenum precursor, carbon source and Mo/C ratios were explored. The materials were characterized using different techniques, such as adsorption/desorption of N2, XRD, Raman spectroscopy, SEM-EDX, TEM-EELS, H2-TPR and XPS. Depending on the preparation method used, the presence of different MoxC crystalline phases, Mo2C and/or MoC cubic and/or hexagonal, were determined. The catalytic behaviour in CO2 conversion for CO production through the reverse water gas shift reaction was tested using a reactant mixture CO2/H2 = 1/3 (molar ratio) at 0.1 MPa and a gas hourly space velocity of 3000 h-1. Values of CO2 conversion up to 26 %, with nearly 100 % selectivity to CO were achieved as a function of the reaction temperature and the catalyst used

Effective and highly selective CO generation from CO2 using a polycrystalline α‑Mo2C catalyst

Present experiments show that synthesized polycrystalline hexagonal α-Mo2C is a highly efficient and selective catalyst for CO2 uptake and conversion to CO through the reverse water gas shift reaction. The CO2 conversion is ~16% at 673 K, with selectivity towards CO > 99%. CO2 and CO adsorption is monitored by DRIFTS, TPD, and microcalorimetry, and a series of DFT based calculations including the contribution of dispersion terms. The DFT calculations on most stable model surfaces allow for identifying numerous binding sites present on the catalyst surface, leading to a high complexity in measured and interpreted IR- and TPD-spectra. The computational results also explain ambient temperature CO2 dissociation towards CO as resulting from the presence of surface facets such as Mo2C(201)-Mo/C ¿displaying Mo and C surface atoms¿ and Mo-terminated Mo2C(001)-Mo. An ab initio thermodynamics consideration of reaction conditions however demonstrates that these facets bind CO2 and CO + O intermediates too strong for a subsequent removal, whereas the Mo2C(101)-Mo/C exhibits balanced binding properties, serving a possible explanation of the observed reactivity. In summary, results show that polycrystalline α-Mo2C is an economically viable, highly efficient, and selective catalyst for CO generation using CO2 as a feedstock

Exploring the 3D printing of molybdenum carbide-based catalysts for the reverse water gas shift reaction: A multi scale study

A new methodology for preparing 3D printing molybdenum carbide-based catalysts with direct ink writing is presented. CO2 conversion experiments through the reverse water gas shift reaction showed that the catalytic behavior of 3D-MoxC/Al2O3 catalysts is controlled by the crystallite size and crystalline phase, which in turn were dependent on the Mo loading. The formation of cubic δ-MoC and hexagonal η-Mo3C2 was prevalent in small crystallite sizes at low loading of Mo, and α/β-Mo2C in larger crystallite sizes at high loading of Mo. Operando DRIFTS experiments points out that hydroxyl species present on the surface of Al2O3 play a major role in bicarbonate formation that leads to the formation of formates, which eventually decomposes to CO and H2O. The produced structures were mechanically stable and kept their structural and textural properties after reaction. Therefore, this work introduces new perspectives for scaling-up 3D printed structures based on molybdenum carbide

Monitoring the insertion of Pt into Cu2−xSe nanocrystals: a combined structural and chemical approach for the analysis of new ternary phases

The tuning of the chemical composition in nanostructures is a key aspect to control for the preparation of new multifunctional and highly performing materials. The modification of Cu2−xSe nanocrystals with Pt could provide a good way to tune both optical and catalytic properties of the structure. Although the heterogeneous nucleation of metallic Pt domains on semiconductor chalcogenides has been frequently reported, the insertion of Pt into chalcogenide materials has not been conceived so far. In this work we have explored the experimental conditions to facilitate and enhance the insertion of Pt into the Cu2−xSe nanocrystalline lattice, forming novel ternary phases that show a high degree of miscibility and compositional variability. Our results show that Pt is mainly found as a pure metal or a CuPt alloy at high Pt loads (Pt : Cu atomic ratio in reaction medium >1). However, two main ternary CuPtSe phases with cubic and monoclinic symmetry can be identified when working at lower Pt : Cu atomic ratios. Their structure and chemical composition have been studied by local STEM-EDS and HRTEM analyses. The samples containing ternary domains have been loaded on graphite-like C3N4 (g-C3N4) semiconductor layers, and the resulting nanocomposite materials have been tested as promising photocatalysts for the production of H2 from aqueous ethanolic solutions

Antitumor Necrosis Factor Agents to Treat EndoscopicPostoperative Recurrence of Crohn’s Disease: A Nationwide Study With Propensity-Matched Score Analysis

INTRODUCTION:Patients with Crohn's disease experiencing endoscopic postoperative recurrence (POR) may benefit from antitumor necrosis factor (TNF) agents but scarce data on this are available. Our aim was to assess the efficacy of anti-TNF in improving mucosal lesions in patients with endoscopic POR.METHODS:Multicenter, retrospective, study of patients with Crohn's disease who underwent therapy with anti-TNF agents for endoscopic POR (Rutgeerts score > i1). Treatment outcomes were assessed by the findings in the last ileocolonoscopy performed after anti-TNF therapy was initiated. Endoscopic improvement and remission were defined as any reduction in the baseline Rutgeerts score and by a Rutgeerts score < i2, respectively.RESULTS:A total of 179 patients were included, 83 were treated with infliximab and 96 with adalimumab. Median time on anti-TNF therapy at the last endoscopic assessment was 31 months (interquartile range, 13-54). Endoscopic improvement was observed in 61%, including 42% who achieved endoscopic remission. Concomitant use of thiopurines and treatment with infliximab were associated with endoscopic improvement (odds ratio [OR] 2.15, 95% confidence interval [CI] 1.04-4.46; P = 0.03, and OR 2.34, 95% CI 1.18-4.62; P < 0.01, respectively) and endoscopic remission (OR 3.16, 95% CI 1.65-6.05; P < 0.01, and OR 2.01, 95% CI 1.05-3.88; P = 0.04, respectively) in the multivariable logistic regression analysis. These results were confirmed in a propensity-matched score analysis.DISCUSSION:In patients with endoscopic POR, anti-TNF agents improve mucosal lesions in almost two-thirds of the patients. In this setting, concomitant use of thiopurines and use of infliximab seem to be more effective in improving mucosal lesions.Fiorella Canete received a research grant from the Societat Catalana de Digestologia

Effectiveness and Safety of the Sequential Use of a Second and Third Anti-TNF Agent in Patients With Inflammatory Bowel Disease: Results From the Eneida Registry

Background: The effectiveness of the switch to another anti-tumor necrosis factor (anti-TNF) agent is not known. The aim of this study was to analyze the effectiveness and safety of treatment with a second and third anti-TNF drug after intolerance to or failure of a previous anti-TNF agent in inflammatory bowel disease (IBD) patients. Methods: We included patients diagnosed with IBD from the ENEIDA registry who received another anti-TNF after intolerance to or failure of a prior anti-TNF agent. Results: A total of 1122 patients were included. In the short term, remission was achieved in 55% of the patients with the second anti-TNF. The incidence of loss of response was 19% per patient-year with the second anti-TNF. Combination therapy (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.8-3; P < 0.0001) and ulcerative colitis vs Crohn's disease (HR, 1.6; 95% CI, 1.1-2.1; P = 0.005) were associated with a higher probability of loss of response. Fifteen percent of the patients had adverse events, and 10% had to discontinue the second anti-TNF. Of the 71 patients who received a third anti-TNF, 55% achieved remission. The incidence of loss of response was 22% per patient-year with a third anti-TNF. Adverse events occurred in 7 patients (11%), but only 1 stopped the drug. Conclusions: Approximately half of the patients who received a second anti-TNF achieved remission; nevertheless, a significant proportion of them subsequently lost response. Combination therapy and type of IBD were associated with loss of response. Remission was achieved in almost 50% of patients who received a third anti-TNF; nevertheless, a significant proportion of them subsequently lost response