Bernard Delmon

Catalytic removal of NO

The aim of this paper is to review the catalytic reactions for the removal of NO and, more particularly, to discuss the reduction of NO in the presence of NH3, CO, H-2 or hydrocarbons as well as the decomposition of NO. The nature of the different active species, their formation due to dispersion and their interaction with different supports as well as the corresponding correlations with catalytic performance are also discussed. Another goal of this review is to explain the mechanism and kinetics of these reactions on different surfaces as well as the catalyst stability

Study of the Hydrodeoxygenation of Carbonyl, Carboxylic and Guaiacyl Groups Over Sulfided Como/gamma-al2o3 and Nimo/gamma-al2o3 Catalysts .1. Catalytic Reaction Schemes

The elimination of specific oxygenated groups of biomass-derived pyrolysis oils (bio-oils) is necessary for improving their stability. These are mainly unsaturated groups like alkene, carbonyl and carboxylic functions, as well as guaiacyl groups. For practical applications, it is desirable that the reactions are performed selectively in order to avoid excessive hydrogen consumption. The reactions must be done at relatively low temperature in order to limit competitive thermal condensation reactions. In this study, model oxygenated compounds were used, namely 4-methylacetophenone, diethyldecanedioate and guaiacol. They were tested simultaneously in one reaction test in the presence of sulfided cobalt-molybdenum and nickel-molybdenum supported on gamma-alumina catalysts in a batch system. Their reactivity and conversion scheme were determined. The ketonic group is easily and selectively hydrogenated into a methylene group at temperatures higher than 200 degrees C. Carboxylic groups are also hydrogenated to methyl groups, but a parallel decarboxylation occurs at comparable rates. A temperature around 300 degrees C is required for the conversion of carboxylic groups as well as for the conversion of the guaiacyl groups. The main reaction scheme of guaiacol is its transformation in hydroxyphenol which is subsequently converted to phenol. But in batch reactor conditions, guaiacol gives a high proportion of heavy products. CoMo and NiMo catalysts have comparable activities and selectivities. However, the NiMo catalyst has a higher decarboxylating activity than CoMo and also leads to a higher proportion of heavy products during the conversion of guaiacol.

Phase Cooperation and Remote-control Effects in Selective Oxidation Catalysts

This review paper concerns allylic oxidations and oxidative dehydrogenations. The corresponding catalysts often contain two or several oxide phases. The objective is to discuss the possible reasons why these phases cooperate (act synergetically). Different interpretations are reviewed. The authors discuss in detail the evidence showing that the synergy is often due to remote control. In such a mechanism, one phase, the donor, dissociates oxygen to form a surface mobile species which spills over to the other phase, or acceptor. The acceptor is the potentially active phase. This phase needs to be irrigated by spill-over oxygen to exhibit maximum activity and selectivity. The various modifications of the acceptor brought about by spill-over oxygen are discussed: maintaining the acceptor at a high oxidation state, preventing the destruction of the structure of the acceptor, and inhibiting the formation of carbonaceous deposits or coke precursors. Parallel experiments with the same two-phase catalysts catalysing an oxygen aided dehydration suggest that the role of spill-over oxygen is to protect some Bronsted acidity of the acceptor. This interpretation of the cooperation between phases permits definite roles to be attributed to the oxide phases present in multicomponent catalysts and to measure approximately their ability to act as donors or acceptors.

Influence of Water in the Deactivation of a Sulfided Nimo Gamma-al2o3 Catalyst During Hydrodeoxygenation

Water and oxygenated compounds are generally viewed as highly detrimental to the stability of sulfided hydrotreating catalysts. In this paper, a sulfided NiMo/gamma-Al2O3 catalyst was treated in a batch reactor under typical hydrotreating conditions with or without water vapor. Changes of the HDO activity, composition, and texture of the various catalyst samples were further evaluated. Catalyst samples used in the HDO of organic oxygenated compounds were also characterized by XPS for modifications of the chemical surface composition. Water caused a decrease of the catalytic activity to one-third the activity of the fresh catalyst but did not change the hydrogenation-hydrogenolysis selectivity. Water was also the cause of a small loss of the specific surface area conjugated to some crystallization of the gamma-alumina support in a hydrated boehmite phase. On the other hand, the metal content, the dispersion, and the sulfidation state were not specifically affected by water. The deactivation would rather be related to the appearance of oxidized nickel species. The observations can be interpreted as resulting from the formation of an inactive nickel sulfate layer covering the active sulfide phases or from the formation of nickel aluminate. Otherwise, the oxidation of the molybdenum sulfide phase by water or oxygenated compounds in reaction conditions is very limited

Study of the Hydrodeoxygenation of Carbonyl, Carboxylic and Guaiacyl Groups Over Sulfided Como/gamma-al2o3 and Nimo/gamma-al2o3 Catalyst .2. Influence of Water, Ammonia and Hydrogen-sulfide

The hydrotreatment of various oxygenated groups (ketonic, carboxylic, methoxyphenol) present in bio-oils in the presence of CoMo and NiMo catalysts was studied in a batch reactor using a mixture of model compounds mimicking the real feed. The influence of potential poisons or inhibitors of the reactions (water, ammonia and hydrogen sulfide) was determined. High quantities of water had only a very slight inhibiting effect on the reactions. Ammonia strongly inhibited the conversion of carboxylic esters and the removal of the methoxy group of guaiacol, but, surprisingly, the hydrogenation of the ketonic group was not affected. Hydrogen sulfide depressed the activity of the NiMo catalyst for the conversion of the ketonic group but not that of the CoMo catalyst. It had an enhancing effect on the conversion of the carboxylic ester group and no effect on the removal of the methoxy group of guaiacol. The evolution of activities and selectivities as a function of the concentration of potential inhibitors provided an indication of the catalytic sites responsible for the various reactions. The absence of the influence of ammonia on the hydrogenation of the ketonic group was interpreted as resulting from the participation of nucleophilic sites and hydridic species in the reaction mechanism. Carboxylic esters seem to react on electrophilic sites. Bronsted acids were thought to be responsible for decarboxylation, while uncoordinated metal atoms and sulfhydryl groups could be responsible for the hydrogenation of carboxylic groups. On the other hand, the surface of the alumina support catalyzes the hydrolysis of carboxylic esters into acids. The demethylation of guaiacol occurs for a large part on the Lewis acid-base sites of the gamma-alumina support. The use of hydrogen sulfide and ammonia shows a high potential for controlling the selectivity of reactions occurring in bio-oils hydrotreatment. The present results give hope that the deoxygenation of carboxylic groups could be selectively performed through decarboxylation thanks to catalyst selection and control of the hydrogen sulfide pressure. Ketonic groups and aldehydic groups could be selectively eliminated from complex feeds by applying a pressure of ammonia which would inhibit all reactions but hydrogenation.

Hydrotreatment of pyrolysis oils from biomass : reactivity of the various categories of oxygenated compounds and preliminary techno-economical study

This paper describes essential aspects of the hydrotreatment of pyrolytic oils in the light of results obtained until now at the Universite Catholique de Louvain. Stability of pyrolysis oils necessitates a two-step processing. A low temperature hydrotreatment enables stabilization through reactions like olefin, carbonyl and carboxylic groups reduction. Further hydrotreatment aims at hydrodeoxygenation of phenols and hydrocracking of larger molecules. Results about catalysts, reaction conditions and parameters enabling or influencing the control of the reaction are summarized. Based on these laboratory data, a preliminary techno-economical evaluation is made. 50 wt.-% yields in hydrocarbons for deep hydrorefining of pyrolysis oils can be expected. Nevertheless, a moderate hydroconversion with partial elimination of oxygen would be, economically, more advantageous.

Evidence of phase cooperation in the LaCoO3–CeO2–Co3O4 catalytic system in relation to activity in methane combustion

The objective of this work is to understand the role of physicochemical properties of LaCoO3-CeO2-Co3O4 system with particular attention to the importance of phase segregation. The catalytic materials used were all prepared by the citrate method. They comprised: (i) single phase simple oxides and perovskites; (ii) in situ formed multiphase oxides of nominal compositions La1-xCexCoO3 (x = 0-0.5) prepared from a single solution precursor: (iii) lanthanum-cobalt mixed oxides impregnated with ceria by using cerium trinitrate; and (iv) mechanical mixtures of LaCoO3, CeO2 and Co3O4. Most of the materials were characterized by several methods (XRD, XPS, TPD-O-2). The activity of all of them was determined under the same conditions, using 0.1 g catalyst, 1% methane in air at a flowrate of 75 ml/min. Partial replacement of lanthanum by cerium in LaCoO3 results in a significant improvement of activity, which can only partially be explained by the formation of a defective, perovskite related structure permitting higher oxygen mobility. In La1-xCexCoO3 compositions with x > 0.05, segregation of ceria and other phases occurs. The corresponding high activity seems to result from cooperation between the phases. Some phase cooperation appears to occur even in the mechanically blended mixtures of LaCoO3-CeO2-Co3O4. While phase cooperation is well known in the case of partial oxidation catalysts, it had not been yet explicitly proposed as such in the case of total oxidation (combustion) catalysis

Titania-modified Hydrodesulfurization Catalysts .1. Effect of Preparation Techniques On Morphology and Properties of Tio2-al2o3 Carrier

Abstract Samples of titania—alumina of various compositions were prepared by the following methods: precipitation from TiCl4 solution with aqueous ammonia, impregnation, evaporation from titanium isoproxide solution in isopropanol, and grafting by reaction of TiCl4 with a hydroxy group on Al2O3. BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and analytical electron microscopy (AEM) techniques were used to characterize the state of dispersion TiO2 and Al2O3. The results showed that a homogeneous dispersion of TiO2 and Al2O3 could be obtained by the grafting technique. The impregnation method could also result in an almost perfectly homogeneous distribution. For TiO2—Al2O3 samples deposited by precipitation, the coverage of TiO2 was less than 50% monolayer. Temperature programmed desorption (TPD) measurements of ammonia indicated that the acid sites of Al203 modified by TiO2 experienced a strong influence only for the sample prepared by the grafting technique.

Remote control of catalytic sites by spillover species: A chemical reaction engineering approach

Introduction Evidence has accumulated in the last 20 years that spillover processes play a crucial role in many catalytic phenomena. Four symposia have highlighted the advances of knowledge in this area, and the progressive recognition that the phenomena have extremely important consequences (Delmon et al., 1973; Inui et al., 1993; Pajonk et al., 1983; Steinberg, 1989). In spite of this, very few kinetic models incorporating spillover have been presented. Little attention, if any, is given to these phenomena in the design of processes or in the definition of operating conditions. ∗Review based on a lecture presented at the 13th Colloquim on Chemical Reaction Engineering (13 CCRE), held in Windsor Castle, U.K., and jointly organized by the Working Parties “Chemical Reaction Engineering” and “Chemical Engineering in the Applications of Catalysis” of the European Federation of Chemical Engineering.

New Technical Challenges and Recent Advances in Hydrotreatment Catalysis - a Critical Updating Review

The petroleum industry gets confronted with more stringent requirements with respect to transportation fuels: diminution by a factor of 10, or more, of the sulphur content, and a drastic diminution of the aromatic content. Besides, the quality of the crude oil supply keeps diminishing on an average. For this, the hydrotreating processes (HDS, HDN, HDM, hydrogenation, hydrocracking) will occupy a still increasing place in the refining processes. In a first part, we shall select some of the most important results published recently: use of new modifiers and supports (TiO2, ZrO2, mixed oxides), of metals not yet used in hydrotreating (Ru, Rh, Pd, Pt, possibly Nb, associations RuU, PdU, VU etc.), confirmation of the existence of distinct catalytic sites (hydrogenation and hydrogenolysis of the heteroatom-carbon bonds). Other new results should contribute to clarify the controversies and uncertainties concerning the origin of synergy between different elements and the changes of selectivity as a function of the experimental conditions. For this last topic, reference shall be made to the CoMoS model and the remote control theory. In a second part, we shall summarise the new constraints that the hydrotreating processes will face. It will be necessary to save still more energy. It will also be necessary to achieve a better balance of the various reactions taking place in a given process. The overall selectivity of catalysts and processes will have to be improved. In the third part, we shall try to emphasize directions of research which could help reach the objectives. We shall shortly outline the future contributions of chemical engineering. We shall examine with more details the problems concerning the genesis of adequate catalytic sites (underlining the enormous influence of the activation steps) and the modification of activity by means of the composition of the reacting medium. As the problem of synergy remains crucial for the future developments, we shall also present results with new synergetic systems (WS2 + supported Rh or Pd; MoS2 + supported Pt). The new results give hope that the mechanisms of synergy could get clarified in the near future.