Mechanochemically Prepared Co3O4-CeO2 Catalysts for Complete Benzene Oxidation

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mixed oxides (20, 30, and 40 wt.% of ceria) synthesized by the more sustainable, in terms of less waste, less energy and less hazard, mechanochemical mixing of cerium hydroxide and cobalt hydroxycarbonate precursors. The catalysts were characterized by BET, powder XRD, H2-TPR, UV resonance Raman spectroscopy, and XPS techniques. The mixed oxides exhibited superior catalytic activity in comparison with Co3O4, thus, confirming the promotional role of ceria. The close interaction between Co3O4 and CeO2 phases, induced by mechanochemical treatment, led to strained Co3O4 and CeO2 surface structures. The most significant surface defectiveness was attained for 70 wt.% Co3O4-30 wt.% CeO2. A trend of the highest surface amount of Co3+, Ce3+ and adsorbed oxygen species was evidenced for the sample with this optimal composition. The catalyst exhibited the best performance and 100% benzene conversion was reached at 200 °C (relatively low temperature for noble metal-free oxide catalysts). The catalytic activity at 200 °C was stable without any products of incomplete benzene oxidation. The results showed promising catalytic properties for effective VOCs elimination over low-cost Co3O4-CeO2 mixed oxides synthesized by simple and eco-friendly mechanochemical mixing.

Catalytic Abatement of VOCs: Aerobic Combustion of Methane or Ethane over Alumina-Supported Metal Oxides Recovered from Spent Catalysts

γ-Al2O3 supported Cu, Cu-Zn and Cu-Ni-Fe-Zn oxide catalysts were prepared using leachate transition metal nitrate and sulfate aqueous solutions from commercial spent catalysts. A bench-scale rig was used to investigate the combustion activity of these catalysts toward methane or ethane in the air stream (1000 ppmv) at a space velocity of 20,000 h-1. The Cu-Ni-Fe-Zn oxides/γ-Al2O3 catalyst proved to be the most active catalyst for the combustion of methane in the temperature range 290-575°C and of ethane in the lower temperature range of 275-525oC as compared to Cu and Cu-Zn oxide loaded catalysts. X-ray powder diffractograms indicated that the metal oxide species were highly dispersed or amorphous on the alumina surface in all the catalysts except for the detection of a minority phase of monoclinic CuO on the Cu-containing mono-metallic catalysts. The co-existence of ZnO in the CuO catalysts suppresses the activity of the copper oxide species and, therefore, the conversion of methane or ethane was reduced. The present research endeavor provides proof-of-concept that relatively inexpensive metal oxide-based heterogeneous catalysts for VOCs abatement can be recovered from spent catalysts. Hence, environmental and health threats of improper handling of VOCs or spent catalysts may be alleviated.

The Use of Zeolites for VOCs Abatement by Combining Non-Thermal Plasma, Adsorption, and/or Catalysis: A Review

Non-thermal plasma technique can be easily integrated with catalysis and adsorption for environmental applications such as volatile organic compound (VOC) abatement to overcome the shortcomings of individual techniques. This review attempts to give an overview of the literature about the application of zeolite as adsorbent and catalyst in combination with non-thermal plasma for VOC abatement in flue gas. The superior surface properties of zeolites in combination with its excellent catalytic properties obtained by metal loading make it an ideal packing material for adsorption plasma catalytic removal of VOCs. This work highlights the use of zeolites for cyclic adsorption plasma catalysis in order to reduce the energy cost to decompose per VOC molecule and to regenerate zeolites via plasma.

Ag/CeO2 Composites for Catalytic Abatement of CO, Soot and VOCs

Nowadays catalytic technologies are widely used to purify indoor and outdoor air from harmful compounds. Recently, Ag–CeO2 composites have found various applications in catalysis due to distinctive physical-chemical properties and relatively low costs as compared to those based on other noble metals. Currently, metal–support interaction is considered the key factor that determines high catalytic performance of silver–ceria composites. Despite thorough investigations, several questions remain debating. Among such issues, there are (1) morphology and size effects of both Ag and CeO2 particles, including their defective structure, (2) chemical and charge state of silver, (3) charge transfer between silver and ceria, (4) role of oxygen vacancies, (5) reducibility of support and the catalyst on the basis thereof. In this review, we consider recent advances and trends on the role of silver–ceria interactions in catalytic performance of Ag/CeO2 composites in low-temperature CO oxidation, soot oxidation, and volatile organic compounds (VOCs) abatement. Promising photo- and electrocatalytic applications of Ag/CeO2 composites are also discussed.