Leslaw Mleczko

Bio: Leslaw Mleczko is an academic researcher from Bayer. The author has contributed to research in topics: Catalysis & Hydrogen chloride. The author has an hindex of 27, co-authored 256 publications receiving 2814 citations. Previous affiliations of Leslaw Mleczko include Novus International & Bayer MaterialScience.

Comprehensive Kinetics of Oxidative Coupling of Methane over the La2O3/CaO Catalyst

Abstract: A comprehensive 10-step kinetic model of the oxidative coupling of methane to C2+ hydrocarbons over a La2O3/CaO catalyst was developed on the basis of kinetic measurements in a microcatalytic fixed-bed reactor covering a wide range of reaction conditions (1 < pO2 < 20 kPa, 10 < pCH4 < 95 kPa, 700 < T < 955 °C, 0.76 mCat/VSTP ≤ 250 kg·s/m3). The reaction scheme contains three primary and seven consecutive steps. The conversion of hydrocarbons and of carbon monoxide with oxygen were described by applying Hougen−Watson type rate equations. For the other reactions power-law rate equations were used. From the experimental data kinetic parameters, i.e. frequency factors, apparent activation energies, and adsorption enthalpies, were estimated. With the kinetic model the experimentally determined conversions of methane and oxygen, as well as yields to C2 hydrocarbons and carbon oxides, could be predicted with an average accuracy of ±20%.

Sustainable chlorine recycling via catalysed HCl oxidation: from fundamentals to implementation

Abstract: The heterogeneously catalysed oxidation of HCl to Cl2 comprises a sustainable route to recover chlorine from HCl-containing streams in the chemical industry. Conceived by Henry Deacon in 1868, this process has been rejuvenated in the last decade due to increased chlorine demand and the growing excess of by-product HCl from chlorination processes. This reaction suffered from many sterile attempts in the past two centuries to obtain sufficiently active and durable catalysts. Intense research efforts have culminated in the recent industrial implementation of RuO2-based catalysts for HCl oxidation. This paper reviews the new generation of technologies for chlorine recycling under the umbrella of Catalysis Engineering, that is, tackling the microlevel (catalyst design), mesolevel (reactor design), and macrolevel (process design). Key steps in the development are emphasised, including lab-scale catalyst screening, advanced catalyst characterisation, mechanistic and kinetic studies over model and real systems, strategies for large-scale catalyst production, mini-plant tests with a technical catalyst, and reactor design. Future perspectives, challenges, and needs in the field of catalysed Cl2 production are discussed. Scenarios motivating the choice between catalysed HCl oxidation and HCl electrolysis or their integration for optimal chlorine recycling technology are put forward.

Kinetic and Reaction Engineering Studies of Dry Reforming of Methane over a Ni/La/Al2O3 Catalyst

Abstract: Kinetic studies of CO2 reforming of methane over a highly active Ni/La/α-Al2O3 catalyst were performed in an atmospheric microcatalytic fixed-bed reactor The reaction temperature was varied between 700 and 900 °C, while partial pressures of CO2 and CH4 ranged from 16 to 40 kPa From these measurements kinetic parameters were determined; the activation energy amounted to 90 kJ/mol The rate of CO2 reforming was described by applying a Langmuir−Hinshelwood rate equation The developed kinetics was interpreted with a two-phase model of a fluidized bed The predictions for a bubbling-bed reactor operated with an undiluted feed (CH4:CO2 = 1:1) at 800 °C showed that, on an industrial scale, significantly longer contact times (Hmf = 78 m, mcat/VSTP = 318 g·s·mL-1) are necessary for achieving thermodynamic equilibrium (XCH4 = 882%, XCO2 = 936%) The performance of the reactor was strongly influenced by the interphase gas exchange: the highest space time yields were obtained for small particles (dp = 80 μm)

Natural Gas to Fuels and Chemicals: Improved Methane Aromatization in an Oxygen-Permeable Membrane Reactor†

Abstract: Adding value with membranes: Improved methane aromatization was achieved by using an oxygen-permeable membrane. The resulting membrane reactor shows a superior methane conversion and a higher resistance towards catalyst deactivation.

Mechanisms of catalyst deactivation

Abstract: The literature treating mechanisms of catalyst deactivation is reviewed. Intrinsic mechanisms of catalyst deactivation are many; nevertheless, they can be classified into six distinct types: (i) poisoning, (ii) fouling, (iii) thermal degradation, (iv) vapor compound formation accompanied by transport, (v) vapor-solid and/or solid-solid reactions, and (vi) attrition/crushing. As (i), (iv), and (v) are chemical in nature and (ii) and (v) are mechanical, the causes of deactivation are basically three-fold: chemical, mechanical and thermal. Each of these six mechanisms is defined and its features are illustrated by data and examples from the literature. The status of knowledge and needs for further work are also summarized for each type of deactivation mechanism. The development during the past two decades of more sophisticated surface spectroscopies and powerful computer technologies provides opportunities for obtaining substantially better understanding of deactivation mechanisms and building this understanding into comprehensive mathematical models that will enable more effective design and optimization of processes involving deactivating catalysts. © 2001 Elsevier Science B.V. All rights reserved.

A review of dry (CO2) reforming of methane over noble metal catalysts

Abstract: Dry (CO2) reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. This reaction produces syngas that can be used to produce a wide range of products, such as higher alkanes and oxygenates by means of Fischer–Tropsch synthesis. DRM is inevitably accompanied by deactivation due to carbon deposition. DRM is also a highly endothermic reaction and requires operating temperatures of 800–1000 °C to attain high equilibrium conversion of CH4 and CO2 to H2 and CO and to minimize the thermodynamic driving force for carbon deposition. The most widely used catalysts for DRM are based on Ni. However, many of these catalysts undergo severe deactivation due to carbon deposition. Noble metals have also been studied and are typically found to be much more resistant to carbon deposition than Ni catalysts, but are generally uneconomical. Noble metals can also be used to promote the Ni catalysts in order to increase their resistance to deactivation. In order to design catalysts that minimize deactivation, it is necessary to understand the elementary steps involved in the activation and conversion of CH4 and CO2. This review will cover DRM literature for catalysts based on Rh, Ru, Pt, and Pd metals. This includes the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.

Photocatalytic Carbon-Nanotube–TiO2 Composites

Abstract: The literature and advances in photocatalysis based on the combination of titania (TiO2) and carbon nanotubes is presented. The semiconductor basis for photocatalysis is introduced for anatase and rutile. Furthermore, the proposed mechanisms of catalytic enhancement resulting from the pairing of the titania semiconductor with either metallic, semiconducting, or defect-rich carbon nanotubes (CNT) is discussed. Differences are apparent for the mixtures and chemically bonded CNT–TiO2 composites. The article then highlights the recent advances in the synthesis techniques for these composites and their photocatalytic reactions with organic, inorganic, and biological agents. Finally, various applications and challenges for these composite materials are reported.

The Hitchhiker's Guide to Flow Chemistry

Abstract: Flow chemistry involves the use of channels or tubing to conduct a reaction in a continuous stream rather than in a flask Flow equipment provides chemists with unique control over reaction parameters enhancing reactivity or in some cases enabling new reactions This relatively young technology has received a remarkable amount of attention in the past decade with many reports on what can be done in flow Until recently, however, the question, “Should we do this in flow?” has merely been an afterthought This review introduces readers to the basic principles and fundamentals of flow chemistry and critically discusses recent flow chemistry accounts

Heterogeneous Catalyst Deactivation and Regeneration: A Review

Abstract: Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.