Lachezar A. Petrov

Hydrogen production by ammonia decomposition using high surface area Mo2N and Co3Mo3N catalysts

High surface area bulk molybdenum nitride catalysts were synthesized via temperature-programmed ammonolysis of an ammonium heptamolybdate and citric acid (CA) composite. The synthesized materials were tested for COx-free H2 production via ammonia decomposition for fuel cell application. Cobalt was added at different loadings (1, 3, and 5 wt%) as a promoter for the bulk molybdenum nitrides. The chemical composition and surface morphology of the nitride catalysts were studied by means of XRD, XPS, SEM-EDAX and TEM techniques. Addition of cobalt increased the formation of the γ-Mo2N phase and cobalt existed as the Co3Mo3N phase, which was uniformly distributed over Mo2N as evidenced by TEM and SEM analyses. A drastic increase in Mo2N crystal size was observed when the Co loading exceeded 3 wt%, which in turn decreased the catalyst activity for ammonia decomposition reaction. All catalysts exhibit higher activity than the reported nitride catalysts at low temperatures. All catalysts showed stable activity for 30 hours. The activation energy calculated for ammonia decomposition was decreased drastically from 131.2 to 99 kJ mol−1 by the addition of cobalt (1 wt%) in Mo2N preparation.

Reaction Mechanism and Deactivation Modes of Heterogeneous Catalytic Systems

Solving the problem of catalyst deactivation is essential in process design. To do this, various aspects of the kinetics of processes with catalyst deactivation, and their different mechanisms, are discussed. Catalyst deactivation often cannot be avoided, but more knowledge on its mechanism can help to find kinetic means to reduce its harmful consequences. When deactivation is caused by coke, the generation of coke precursors is the determining step in the deactivation kinetics. Different types of deactivation were distinguished that lead to different evolution of the process. The phenomenon of non-uniform coking can be linked to catalyst surface non-uniformity. For the class of catalysts with more than one type of active sites, an explanation was suggested for the observed trends in the deactivation modes. For catalytic processes using catalyst particles of industrial size, the influence of intraparticle diffusion resistance is important. The analysis showed that for a number of processes, the decrease of the reaction rate due to deactivation is less under diffusion control. For certain reaction mechanisms, there exist operation conditions where the rate of the process under diffusion control exceeds the rate in the kinetic control regime. A significant problem is the change of selectivity in the course of catalyst deactivation. The selectivity may either decrease or increase, and depends on the reaction mechanism during deactivation. The changes are larger when there is no diffusion resistance. The intentional poisoning of catalysts and its influence on catalyst activity and selectivity for the process of ethylene oxide production was discussed.

Mechanical and corrosion behavior of amorphous and crystalline electroless Ni–W–P coatings

Two types of electroless Ni–W–P coatings: nanocrystalline with low P and amorphous with higher P content are investigated. Scanning probe microscopy is applied to study their morphology. Textured nanocrystalline coatings consist of coarse pyramids built of nanometer thick lamellas. The surface morphology of amorphous coatings is much finer and uniform. Nanohardness of all coatings depends on W content. Microhardness is increasing during the heat treatment up to 350xa0°C due to nickel phosphide precipitation affected by tungsten also. The wear resistance of nanocrystalline Ni–W–P coatings is much higher than that of amorphous in spite of the similar tungsten content in both. Lower corrosion resistance of amorphous Ni–W–P coatings is found by weight loss method during long-term immersion in 5xa0% NaCl. Electrochemical tests by potentiodynamic polarization curves in two model corrosion media—solutions of 0.5xa0M H2SO4 and 5xa0% NaCl—are performed. The corrosion of bi-layered Ni–W–P/Ni–P and Ni–W–P/Ni–Cu–P deposits on mild steel is also investigated. The results prove that an electroless Ni–W–P coating on mild steel extremely improves its mechanical and corrosion behavior. It is demonstrated that in addition to deposit’s structure and composition, the distribution and chemical state of alloy ingredients are also responsible for its properties.

Deactivation Modes of Solid Catalysts with Different Active Sites

An approach is suggested to distinguish different types of active sites responsible for different reactions on bifunctional catalysts. The model assumes a non-uniform vulnerability of active sites that depends on their location. Problems on the relationship between the dis- persion of the active phase and selectivity are discussed. The effect of coke formation on the activity change of different sites is analyzed. It is widely recognized that more than one type of active sites can be distinguished on bi- and poly-functional cata- lysts. The detailed study of these catalysts is very important because of their wide application in industrial processes, such as reforming, dehydrogenation, hydrodesulfurization, and hydrodenitrogenation. For this, it is necessary to de- velop kinetic models that reflect the contribution of distinct types of sites that are influenced by their diverse nature and properties. Such published models are still scarce. The presence of active sites of different nature and properties, while facilitating networks of mutually dependent reaction routes, is a challenge to forecasting the overall effects. It is both of academic and practical interest to obtain more de- tailed knowledge on the kinetic effects arising from the spe- cific features of distinct site types, and their correlation with the reaction mechanism. Distinct types of sites may differ by nature, configuration, adsorption ability, contribution to different reactions, vul- nerability, etc. (e.g., (1-5)). Each type is affected in its own way by various deactivation factors. Hence, the complexity of such catalytic systems is not only with the variety of in- teractions and species involved in the reaction network but also with the deactivation functions relevant to the different types of active sites. 1 Approach It is of significance to distinguish the function of catalyst activity (denoted as ϕ(u)) from the deactivation function (denoted by Φ(u)) that describes the rate of activity de- crease. The activity is due to the contributions of groups of active sites. So far, the decrease in activity is most fre- quently described using a function characterizing the cata- lyst activity ϕ(t) at time t defined as the ratio of the rate r(t)

Partial oxidation of methanol over Au/CeO2–ZrO2 and Au/CeO2–ZrO2–TiO2 catalysts

Experimental data on hydrogen production via a partial oxidation of methanol (POM) reaction on Au/ZrO2, Au/CeO2–ZrO2 and Au/CeO2–ZrO2–TiO2 catalysts is presented in this article. The gold catalysts were prepared by a deposition–precipitation (DP) method and characterized by XRF, XRD, H2-TPR, XPS methods N2 adsorption. The activity results show that the catalyst containing 1 wt% gold supported on a CeO2–ZrO2 carrier demonstrates very good hydrogen selectivity and the highest catalytic activity among all tested catalysts. The optimal working temperature established was 375 °C. At this temperature 75.5% hydrogen selectivity was registered. The presence of oxidized gold in the catalysts composition as well as the support redox properties are the major factors controlling the observed catalytic activity.

COBALT SUPPORTED ON CARBON NANOTUBES. AN EFFICIENT CATALYST FOR AMMONIA DECOMPOSITION

Cobalt supported on carbon nanotubes catalyst is much more active in reaction of ammonia decomposition than nickel and iron catalysts. The observed low temperature activity of Co/carbon nanotubes catalysts is promising option for creating of ammonia decomposition catalysts with low working temperatures.

Nanomaterials for renewable energy storage: synthesis, characterization, and applications

1Department of Chemical and Materials Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia 2Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar 3Electrochemical Power Systems Division, CSIR-Central Electrochemical Research Institute, Karaikudi 630006, India 4SABIC Chair in Catalysis, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia 5Game Lab, Chenergy Group, Department of Applied Science and Technology (DISAT), Politecnico Di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

Role of Chemical Kinetics in the Heterogeneous Catalysis Studies

Abstract The paper presents shortly some of the important elements of the theory and of the practical applications of the kinetics of heterogeneous catalytic reactions. Discussed are some of the most important concepts of the kinetics of complex heterogeneous catalytic reactions, methodology of building kinetic models and mathematical treatment of experimental data, influence of heat and mass transfer, types of laboratory reactors, kinetics and nanosized catalysts and others. Examples for use of the kinetic studies for the development and application of industrial catalysts and modeling of industrial reactors are presented.

Re-dispersion of gold supported on a ‘mixed’ oxide support

The ability to reactivate, stabilize and increase the lifetime of gold catalysts by dispersing large, inactive gold nanoparticles to smaller nanoparticles provides an opportunity to make gold catalysts more practical for industrial applications. Previously it has been demonstrated that mild treatment with iodomethane (J. Am. Chem. Soc., 2009, 131, 6973; Angew. Chem. Int. Ed., 2011, 50, 8912) was able to re-disperse gold on carbon and metal oxide supports. In the current work, we show that this technique can be applied to re-disperse gold on a ‘mixed’ metal oxide, namely a mechanical mixture of ceria, zirconia and titania. Characterization was conducted to guage the impact of the iodomethane (CH3I) treatment on a previously sintered catalyst. Graphical Abstract

Ammonia treated Mo/AC catalysts for CO hydrogenation with improved oxygenates selectivity

A series of ammonia treated Mo/Activated Carbon (AC) catalysts were synthesized by wet impregnation method by nominal incorporation of 5, 10 and 15 wt% of molybdenum. The calcined catalysts (