Development of Industrial Catalysts for Sustainable Chlorine Production

The heterogeneously catalyzed gas-phase oxidation of HCl to Cl2 offers an energy-efficient and eco- friendly route to recover chlorine from HCl-containing byproduct streams in the chemical industry. This process has attracted renewed interest in the last decade due to an increased chlorine demand and the growing excess of byproduct HCl from chlorination processes. Since its introduction (by Deacon in 1868) and till recent times, the industrialization of this reaction has been hindered by the lack of sufficiently active and durable materials. Recently, RuO2-based catalysts with outstanding activity and stability have been designed and they are being implemented for large-scale Cl2 recycling. Herein, we review the main limiting features of traditional Cu-based catalysts and survey the key steps in the development of the new generation of industrial RuO2-based materials. As the expansion of this technology would benefit from cheaper, but comparably robust, alternatives to RuO2-based catalysts, a nov el CeO2-based catalyst which offers promising perspectives for application in this field has been introduced

Europium Oxybromide Catalysts for Efficient Bromine Looping in Natural Gas Valorization

ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

An integrated approach to Deacon chemistry on RuO2-based catalysts

AbstractRationally designed RuO2-based Deacon catalysts can contribute to massive energy saving compared to the current electrolysis process in chemically recycling HCl to produce molecular chlorine. Here, we report on our integrated approach between state-of-the-art experiments and calculations. The aim is to understand industrial Deacon catalyst in its realistic surface state and to derive mechanistic insights into this sustainable reaction. We show that the practically relevant RuO2/SnO2 consists of two major RuO2 morphologies, namely 2–4 nm-sized particles and 1–3-ML-thick epitaxial RuO2 films attached to the SnO2 support particles. A large fraction of the small nanoparticles expose {110} and {101} facets, whereas the film grows with the same orientations, due to the preferential surface orientation of the rutile-type support. Steady-state Deacon kinetics indicate a medium-to-strong positive effect of the partial pressures of reactants and deep inhibition by both water and chlorine products. Temporal Analysis of Products and in situ Prompt Gamma Activation Analysis strongly suggest a Langmuir–Hinshelwood mechanism and that adsorbed Cl poisons the surface. Under relevant operation conditions, the reactivity is proportional to the coverage of a specific atomic oxygen species. On the extensively chlorinated surface that can be described as surface oxy-chloride, oxygen activation is the rate-determining step. DFT-based micro-kinetic modeling reproduced all experimental observations and additionally suggested that the reaction is structure sensitive. Out of the investigated models, the 2ML RuO2 film-covered SnO2 gives rise to significantly higher reactivity than the (101) surface, whereas the 1ML film seems to be inactive

Halogen-Mediated Conversion of Hydrocarbons to Commodities

ISSN:0009-2665ISSN:1520-689

Depleted uranium catalysts for chlorine production

This study demonstrates depleted uranium as a remarkable heterogeneous catalyst for the oxidation of HCl to Cl2. This reaction comprises a sustainable approach to valorise byproduct HCl streams in the chemical industry. Bulk α-U3O8 showed an outstanding stability against chlorination, which is crucial for its durability in catalytic tests. UO2 and γ-UO3 transformed into α-U3O8 under reaction conditions. Uranium deposition on different carriers by dry impregnation concluded the superiority of zirconia as support. HAADF-STEM investigations revealed that the uranium oxide on the surface of this carrier is present in the form of a film-like nanostructure with a thickness ranging from a monolayer to 1 nm as well as atomic dispersion. The effect of variables (temperature, feed O2/HCl ratio, metal loading, and Cl2 co-feeding) on the performance of U3O8/ZrO2 has been studied. The HCl conversion over this catalyst increased with reaction time as a likely consequence of in situ re-dispersion of the original uranium phase into atomically dispersed UOx. As demonstrated by H2-TPR, the uranium in the generated UOx phase is more oxidised than in the original U3O8. Such a highly dispersed active phase is produced faster in the uncalcined sample. The extraordinary stable Cl2 production over U3O8/ZrO2 at 773 K for 100 h on stream indicates its potential for application in high-temperature HCl oxidation. Under these conditions, other known catalytic materials suffer from significant deactivation.ISSN:2041-6520ISSN:2041-653

Olefins from Natural Gas by Oxychlorination

ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

Lanthanide compounds as catalysts for the one-step synthesis of vinyl chloride from ethylene

ISSN:0021-9517ISSN:1090-269

Catalytic Oxychlorination versus Oxybromination for Methane Functionalization

The catalytic oxyhalogenation is an attractive route for the functionalization of methane in a single step. This study investigates methane oxychlorination (MOC) and oxybromination (MOB) under a wide range of conditions over various materials having different oxidation properties to assess the effect of hydrogen halide (HX, X = Cl, Br) on the catalyst performance. The oxyhalogenation activity of the catalysts, ranked as RuO₂ > Cu–K–La–X > CeO₂ > VPO > TiO₂ > FePO₄, is correlated with their ability to oxidize the hydrogen halide and the gas-phase reactivity of the halogen with methane. The product distribution is found to be strongly dependent on the nature of the catalyst and the type of halogen. The least reducible FePO₄ exhibits a marked propensity to halomethanes (CH₃X, CH₂X₂), and the strongly oxidizing RuO₂ favors combustion in both reactions, while other systems reveal stark selectivity differences between MOC and MOB. VPO and TiO₂ lead to a selective CH₃Br production in MOB and pronounced CO formation in MOC, whereby product distribution was only slightly affected by the variation of the HX concentration. In contrast, CeO₂ and Cu-based catalysts provide a high selectivity to CH₃Cl but give rise to a marked CO₂ formation when HBr is used as a halogen source. The behavior of the latter systems is explained by the higher energy of the metal–Cl bond in comparison to the metal–Br bond, enabling more suppression of the unwanted CO and CO₂ formation when HCl is used, as also inferred from the more pronounced performance dependence on the HX content in the feed. Extrapolating this result, the highest reported yields of chloromethanes (28% at >82% selectivity) and bromomethanes (20% at >98% selectivity) are attained over CeO₂, by adjusting the feed HX content to curb the CO₂ generation. A vis-à-vis comparison of MOC and MOB presented for the first time in this study deepens the understanding of halogen-mediated methane functionalization as a key step toward the design of an oxyhalogenation process

In situ synchrotron x-ray diffraction studies monitoring mechanochemical reactions of hard materials: Challenges and limitations

In situ monitoring of mechanochemical reactions of soft matter is feasible by synchrotron diffraction experiments. However, so far, reactions of hard materials in existing polymer milling vessels failed due to insufficient energy input. In this study, we present the development of a suitable setup for in situ diffraction experiments at a synchrotron facility. The mechanochemical transformation of boehmite, $γ$-AlOOH, to corundum, $\alpha$-Al$_2$O$_3$, was chosen as a model system. The modifications of the mill’s clamping system and the vessels themselves were investigated separately. Starting from a commercially available Retsch MM 400 shaker mill, the influence of the geometrical adaptation of the setup on the milling process was investigated. Simply extending the specimen holder proved to be not sufficient because changes in mechanical forces need to be accounted for in the construction of optimized extensions. Milling vessels that are suitable for diffraction experiments and also guarantee the required energy input as well as mechanical stability were developed. The vessels consist of a steel body and modular polymer/steel rings as x-ray transparent windows. In addition, the vessels are equipped with a gas inlet and outlet system that is connectable to a gas analytics setup. Based on the respective modifications, the transformation of boehmite to corundum could be observed in an optimized setup