The effect of gold loading on the catalytic oxidation performance of CeO2/H2O2 system

Complete Benzene Oxidation over Mono and Bimetallic Pd—Au Catalysts on Alumina-Supported Y-Doped Ceria

The protection of environment and human health stimulates intensive research for abatement of volatile organic compounds (VOCs) in the atmosphere. Complete catalytic oxidation is an efficient, environmentally friendly and economically feasible method for elimination of VOCs. This study aims to design high performing and cost-effective catalytic formulations by exploration of appropriate and economically viable supports. Alumina-supported ceria (30 wt.%) and Y2O3 (1 wt.%)-doped ceria were prepared by mechanical mixing and were used as support of mono Au (2 wt.%) and Pd (1 wt.%) and bimetallic Pd-Au catalysts. The characterization by textural measurements, X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), EPR (electron paramagnetic resonance) and temperature-programmed reduction (TPR) was carried out in order to clarify the relationship between catalyst composition, textural, structural and surface properties, reducibility and catalytic performance for complete benzene oxidation. Among all studied catalysts, Pd-based catalysts exhibited the best combustion activity. In particular, monometallic Pd on alumina supported Y-doped ceria attained 100% of complete benzene conversion at 180 °C. These catalytic materials have potential to meet stringent emission regulations in an economical and effective way.

Wastewater Treatment by Catalytic Wet Peroxidation Using Nano Gold-Based Catalysts: A Review

Nowadays, there is an increasing interest in the development of promising, efficient, and environmentally friendly wastewater treatment technologies. Among them are the advanced oxidation processes (AOPs), in particular, catalytic wet peroxidation (CWPO), assisted or not by radiation. One of the challenges for the industrial application of this process is the development of stable and efficient catalysts, without leaching of the metal to the aqueous phase during the treatment. Gold catalysts, in particular, have attracted much attention from researchers because they show these characteristics. Recently, numerous studies have been reported in the literature regarding the preparation of gold catalysts supported on various supports and testing their catalytic performance in the treatment of real wastewaters or model pollutants by CWPO. This review summarizes this research; the properties of such catalysts and their expected effects on the overall efficiency of the CWPO process, together with a description of the effect of operational variables (such as pH, temperature, oxidant concentration, catalyst, and gold content). In addition, an overview is given of the main technical issues of this process aiming at its industrial application, namely the possibility of using the catalyst in continuous flow reactors. Such considerations will provide useful information for a faster and more effective analysis and optimization of the CWPO process.

FeNiCeOx ternary catalyst prepared by ultrasonic impregnation method for diclofenac removal in Fenton-like system

FeNiCeO_x was firstly prepared by ultrasonic impregnation method and used to remove diclofenac in a Fenton-like system. The catalytic activity was improved successfully by doping Ni into FeCeO_x. The diclofenac removal efficiency reached 97.9% after 30 min reaction. The surface morphology and properties of FeNiCeO_x were characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Raman and X-ray photoelectron spectroscopy (XPS) analyses. FeNiCeO_x in this paper had larger specific surface area than those prepared by other methods, which was attributed to the cavitation effect and hot-spot effect during the ultrasonic synthesis process. Low crystallinity of Fe₂O₃ and NiO showed by characterization could lead to high interaction of Fe and Ni ions with support of CeO₂. They substituted Ce in CeO₂, caused lattice contraction and formed more oxygen vacancies, which favoured the catalytic reaction. Meanwhile, Fe and Ce ions both had redox cycles of Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺, which facilitated the electron transfer in the reaction. The synergistic effect among Fe, Ni and Ce might lead to better catalytic performance of FeNiCeO_x than any binary metal oxides constituted from the above three elements. Finally, the potential mechanism of diclofenac removal in FeNiCeO_x-H₂O₂ system is proposed.

Ce3+ self-doped CeOx/FeOCl: an efficient Fenton catalyst for phenol degradation under mild conditions

Herein, a novel Ce³⁺ self-doped CeO_x/FeOCl composite was successfully prepared by a facile method for the first time, which showed remarkable catalytic activity as a Fenton catalyst in the degradation of phenol under the conditions of a neutral solution, room temperature and natural light.

Sonocatalytic degradation of diclofenac with FeCeOx particles in water

This paper studies the sonocatalytic degradation of diclofenac in water using FeCeO_x-catalyzed ultrasound. The effects of pre-adsorption and gas addition were investigated. Nitrogen adsorption/desorption, SEM, XRD, Raman and XPS analyses of FeCeO_x before and after sonication were characterized. The proposed mechanism was based on the microstructure changes of FeCeO_x and reactive-species-scavenging performances. The results show that FeCeO_x has excellent performance in catalyzing an ultrasonic system in water, and 80% of diclofenac was removed in 30min ([Diclofenac]=20mg/L, FeCeO_x amount=0.5g/L, pH=6, ultrasonic density=3.0W/cm³, ultrasonic frequency=20kHz, temperature=298K). The Fe, Ce, and O elements remained highly dispersed in the structure of FeCeO_x, and the solid solution structure of FeCeO_x remained stable after the reaction. Ce (III) was gradually oxidized to Ce (IV) and Fe (III) was gradually reduced to Fe (II) after the reaction, which indicates that Fe and Ce ions with different valences coexisted in dynamic equilibrium. The amount of oxygen vacancies in FeCeO_x significantly decreased after the reaction, which indicates that oxygen vacancy participated in the ultrasonic process. Singlet oxygen ¹O₂ was the primary reactive species in the degradation process, and the hydroxyl radicals OH and superoxide radical anion O₂^- also participated in the reaction. FeCeO_x had excellent chemical stability with negligible leaching ions in the ultrasonic process.

Insight into Several Factors that Affect the Conversion between Antioxidant and Oxidant Activities of Nanoceria

Many conflicting results have been reported related to the antioxidant and oxidant activities of nanoceria. On the basis of this research, many factors might affect the antioxidant activity of nanoceria. However, all of the factors reported only affect the antioxidant activity of nanoceria to a limited extent or cause the antioxidant activity to be lost. We found that several factors can induce conversion between the protective effect and toxicity of nanoceria. At low concentrations of hydroxyl radicals (•OH) and nanomaterials, nanoceria exhibited antioxidant activity but could produce greater amounts of •OH at higher •OH or nanomaterial concentrations and subsequently exhibit oxidant activity. Moreover, the morphology and size of nanoceria can also affect this conversion. We found that high concentrations of •OH and nanoceria could introduce a high amount of Ce(3+) in the system, which might be the reason that nanoceria converted from exhibiting antioxidant to oxidant activity. Under this condition, nanoceria act as a catalyst similar to Fe(2+) to promote •OH production in a Fenton system and also as a catalyst promoter to boost Fe(2+) production of additional •OH during the redox reaction. These conclusions support a better understanding of conflicting reports on medicinal applications for nanoceria and promote their practical application.

Preparation of FeCeOx by ultrasonic impregnation method for heterogeneous Fenton degradation of diclofenac

FeCeOx has been successfully synthesized by ultrasonic impregnation method and applied in diclofenac removal in heterogeneous Fenton process. The effects of ultrasonic density, impregnation time, mole ratio of Fe and Ce and calcination temperature were investigated. Nitrogen adsorption/desorption, SEM, XRD, HRTEM, Raman and XPS analyses were characterized. Stability and reusability of FeCeOx were evaluated. The results indicated that 83% degradation efficiency of diclofenac was achieved by FeCeOx under the optimum preparation conditions. Fe ions were distributed uniformly in crystal structure and the solid solution structure of FeCeOx with a lattice constriction was formed. Exposed crystalline plane (200) with a relatively high surface energy may be the main reason to provide high catalytic activity of FeCeOx. Oxygen vacancies took part in catalytic process and a portion of them were oxidized after reaction. FeCeOx showed an excellent chemical stability and reusability in heterogeneous Fenton process.

Facile synthesis of a novel CeO2/glass bead catalyst with enhanced catalytic oxidation performance

It is the first time that the preparation of novel CeO₂/glass bead catalysts with excellent catalytic oxidation activity in organic pollutant degradation have been reported.

Noble metal ions in CeO2 and TiO2: synthesis, structure and catalytic properties

CeO₂ and TiO₂ based noble metal ionic catalysts show very high catalytic activities toward several reactions such as auto exhaust, water gas shift, H₂ + O₂ recombination compared to supported nanometal catalysts due to their electronic interactions.