CO2 Hydrogenation to Methanol over Ce and Zr Containing UiO-66 and Cu/UiO-66

Direct hydrogenation of CO2 to methanol is an interesting method to recycle CO2 emitted e.g., during combustion of fossil fuels. However, it is a challenging process because both the selectivity to methanol and its production are low. The metal-organic frameworks are relatively new class of materials with a potential to be used as catalysts or catalysts supports, also in the reaction of MeOH production. Among many interesting structures, the UiO-66 draws significant attention owing to its chemical and thermal stability, developed surface area, and the possibility of tuning its properties e.g., by exchanging the zirconium in the nodes to other metal cations. In this work we discuss—for the first time—the performance of Cu supported on UiO-66(Ce/Zr) in CO2 hydrogenation to MeOH. We show the impact of the composition of UiO-66-based catalysts, and the character of Cu-Zr and Cu-Ce interactions on MeOH production and MeOH selectivity during test carried out for 25 h at T = 200 °C and p = 1.8 MPa. Significant increase of selectivity to MeOH was noticed after exchanging half of Zr4+ cations with Ce4+; however, no change in MeOH production occurred. It was found that the Cu-Ce coexistence in the UiO-66-based catalytic system reduced the selectivity to MeOH when compared to Cu/UiO-66(Zr), which was ascribed to lower concentration of Cu0 active sites in Cu/UiO-66(Ce/Zr), and this was caused by oxygen spill-over between Cu0 and Ce4+, and thus, the oxidation of the former. The impact of reaction conditions on the structure stability of tested catalyst was also determined.This work was financed by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wrocław University of Technology and the project 0402/0100/17

Catalytic nitrate reduction in water

Nous avons choisi d étudier la conversion catalytique des nitrates dissous qui sont une cause majeure de contamination des eaux. C est un procédé complexe en plusieurs étapes qui suit la réaction : NO3- -> NO2- -> [NO] -> N2 + NH4+ + OH-Le but scientifique de cette thèse a été de déterminer une relation entre la structure physico-chimique des catalyseurs supportés et leur activité et leur sélectivité dans la réduction des nitrates. Les cinétiques de réaction ont également été étudiées en relation avec la structure des catalyseurs supportés Les travaux réalisés ont été axés autour des points suivants : 1. Elaboration des supports de catalyseurs : Deux groupes principaux de matériaux ont été étudiés : des matériaux carbonés et des matériaux inorganiques qui ont été modifiés par un traitement acide ou basique ou par dépôt des oxydes (Al2O3, ZrO2 seuls ou en mélange). 2. Synthèse du catalyseur : Les oxydes de métaux nobles et de transition ont été fixés sur les supports. Des systèmes monométalliques avec Pt et Pd et bimétalliques Pd-Cu ont été étudiés puis caractérisés par de nombreuses techniques. L efficacité des ces supports a été déterminée en fonction de leur activité catalytique. 3. Détermination des propriétés catalytiques : Le rôle et l effet des paramètres tels que nature du support, composition de la phase active, présence de sels inorganiques dans le milieu réactionnel, nature du réducteur sur la vitesse de réduction des nitrates et sélectivité des réactions ont été largement étudiés La discussion générale fait ressortir les combinaisons support/catalyseur les plus efficaces pour la dénitrification des eaux de consommationWe chose to study the catalytic conversion of dissolved nitrate, which are a major cause of water contamination. It is a complex process into several steps following the reaction: NO3- -> NO2-> [NO] -> N2 + NH4+ + + OH- The scientific goal of this thesis was to determine a relationship between the physico-chemical structure of catalysts and their activity and selectivity in the reduction of nitrates. The reaction kinetics were also studied in relation to the structure of catalysts. The work focused around the following points: 1. Preparation of catalyst supports: Two main groups of materials were studied: carbon materials and inorganic materials that have been modified by acid or base treatment or by deposit oxides (Al2O3, ZrO2 alone or in mixture). 2. Synthesis of catalyst: oxides of noble and transition metals have been established on the supports. Systems with monometallic Pt and Pd and bimetallic Pd-Cu have been studied and characterized by many techniques. The effectiveness of these materials was determined depending on their catalytic activity. 3. Determination of the catalytic properties: The role and effect of parameters such as support, type of medium, active phase composition, the presence of inorganic salts in the reaction medium, nature of reducing on the rate of nitrate reduction and selectivity of the reactions were widely studied. The debate highlights the combination support / most effective catalyst for denitrification of drinking waterMETZ-SCD (574632105) / SudocSudocFranceF

Potassium-copper perovskite catalysts for mild temperature diesel soot combustion

The activity and stability of potassium-copper perovskite catalysts for soot combustion were analysed at 450 °C in a NOx/O2 gas mixture. Both impregnated (K-Cu/SrTiO3) and substituted (SrKTiCuO3) copper-potassium catalysts were prepared. For comparative purpose, also a potassium substituted catalyst (SrKTiO3) was studied. The high activity of the fresh potassium catalyst (SrKTiO3) is based on the volatile potassium species reaching the surface of soot. However, this catalyst is not useful because potassium is progressively lost during the reaction. Potassium was stabilized by copper and, as a consequence, the two potassium-copper perovskite catalysts present a constant activity for the soot combustion. The activity of the potassium-copper perovskite catalysts, which is maintained during consecutive reactions, is related to their NO2 production capacity. The metal addition method seems to influence the catalysts performance, the substituted catalyst (SrKTiCuO3) being the most active and stable.The authors gratefully acknowledge the financial support of the Spanish Government (MINECO, Project CTQ2012-030703) and of the FEDER funding