Albin Pintar

Catalytic oxidation of aqueous solutions of organics. An effective method for removal of toxic pollutants from waste waters

Abstract Catalytic liquid-phase oxidation of aqueous solutions of organics is presented as a potential, advanced waste water treatment technology. Catalysts are briefly reviewed first, followed by mechanistic speculations and kinetics that have been proposed for liquid-phase oxidation of some model pollutants. Subsequently, oxidation reactors and potential process schemes are discussed.

Catalytic oxidation of aqueous p-chlorophenol and p-nitrophenol solutions

Abstract Catalytic liquid-phase oxidation of aqueous solutions of substituted phenols ( p -chlorophenol and p -nitrophenol) was studied in a differential, liquid-full operated fixed bed reactor. Experiments were performed in a wide concentration range of both reactants, i.e. dissolved model pollutant and oxygen, at reaction temperatures between 150 and 190°C and total pressure of 30 bar. A proprietary catalyst containing supported copper, zinc and cobalt oxides was found to be effective for converting phenols via intermediates such as benzenedioles, quinones, and the C-4 compounds to carbon dioxide. A proposed intrinsic rate expression for disappearance of phenols is based on the Langmuir-Hinshelwood kinetic formulation, accounting for equilibrium model pollutant as well as dissociative oxygen adsorption processes on different types of active sites, and an initial hydroxyl hydrogen abstraction reaction to be the rate controlling step. The oxidation rates of phenols decrease as the Hammett constants of the substituents become more positive, reflecting trends in the basicity and nucleophilicity of substituted phenols. It is believed that heterogeneously catalysed aqueous-phase oxidation of phenols undergoes a combined redox and nonbranched-chain free-radical mechanism which involves initiation on the catalyst surface and, due to a high solid to liquid ratio in a fixed bed reactor, predominant heterogeneous propagation and termination. The involvement of a free-radical mechanism is indicated by the intermediates formed, and free-radical initiator and inhibitor effects on observed disappearance rates of phenols.

Transition metal pairs on ceria-promoted, ordered mesoporous alumina as catalysts for the CO2 reforming reaction of methane

CoFe, CoW, NiFe and NiW bimetallic pairs deposited over CeO2–ZrO2 promoted ordered mesoporous γ-Al2O3 were tested in the methane dry reforming reaction. The catalysts were characterized by N2 adsorption, wide and small angle XRD, TEM, UV-vis DRS and H2-TPR techniques. Upon thermal treatment, diffusion of Ni and Co into the alumina matrix occurred, resulting in the formation of corresponding aluminate spinels. Based on UV-vis characterization, the formation of bulk Fe2O3 could be only tentatively assigned to the NiFe/AlCZ catalyst. Bulk Co3O4 is likely present in both CoW and CoFe catalysts. CoFe/AlCZ and NiFe/AlCZ catalysts achieved high and stable methane conversion rates of 8.8 and 6.0 mmol of CH4 per gcat per min, respectively. The activity of tungsten-containing catalysts (CoW/AlCZ and NiW/AlCZ) was substantially lower compared to iron-containing catalysts (2.8 and 0.8 mmol of CH4 per gcat per min, respectively) and their deactivation was likely related to sintering and oxidation of active metal clusters. A low carbon content was accumulated on the surface of spent NiFe/AlCZ, CoFe/AlCZ and NiW/AlCZ catalysts after 20 h tests (0.6–1.2 wt%), indicating the high efficiency of the redox promoter under dry reforming conditions.

Low-temperature catalytic decarboxylation of formic and acetic acid over a Ru/TiO2 catalyst: prospects for continuous production of energy-rich gaseous mixtures

Catalytic decarboxylation is a novel and promising pathway for continuous and efficient conversion of organic wastewaters. Stable conversion of acetic acid to CH4 and CO2 mixtures (T ≥ 225 °C, Sp > 80%, 70 h TOS) was demonstrated. Approaches for overcoming catalyst deactivation during production of H2-rich gas from formic acid are outlined.