A Comparative Study of Mn/Co Binary Metal Catalysts Supported on Two Commercial Diatomaceous Earths for Oxidation of Benzene

State of the Art and Challenges in Complete Benzene Oxidation: A Review

Increased levels and detrimental effects of volatile organic compounds (VOCs) on air quality and human health have become an important issue in the environmental field. Benzene is classified as one of the most hazardous air pollutants among non-halogenated aromatic hydrocarbons with toxic, carcinogenic, and mutagenic effects. Various technologies have been applied to decrease harmful emissions from various sources such as petrochemistry, steel manufacturing, organic chemical, paint, adhesive, and pharmaceutical production, vehicle exhausts, etc. Catalytic oxidation to CO2 and water is an attractive approach to VOC removal due to high efficiency, low energy consumption, and the absence of secondary pollution. However, catalytic oxidation of the benzene molecule is a great challenge because of the extraordinary stability of its six-membered ring structure. Developing highly efficient catalysts is of primary importance for effective elimination of benzene at low temperatures. This review aims to summarize and discuss some recent advances in catalyst composition and preparation strategies. Advantages and disadvantages of using noble metal-based catalysts and transition metal oxide-based catalysts are addressed. Effects of some crucial factors such as catalyst support nature, metal particle size, electronic state of active metal, redox properties, reactivity of lattice oxygen and surface adsorbed oxygen on benzene removal are explored. Thorough elucidation of reaction mechanisms in benzene oxidation is a prerequisite to develop efficient catalysts. Benzene oxidation mechanisms are analyzed based on in situ catalyst characterization, reaction kinetics, and theoretical simulation calculations. Considering the role of oxygen vacancies in improving catalytic performance, attention is given to oxygen defect engineering. Catalyst deactivation due to coexistence of water vapor and other pollutants, e.g., sulfur compounds, is discussed. Future research directions for rational design of catalysts for complete benzene oxidation are provided.

Conversion of Geraniol into Useful Value-Added Products in the Presence of Catalysts of Natural Origin: Diatomite and Alum

This article presents research related to the transformation of geraniol (GA), leading to the formation of products with very valuable properties. In the planned method, heterogeneous catalysts of natural origin in the form of alum and diatomite were used as catalysts. Initially, the process which we investigated was the process of isomerization of GA, but it turned out during the studies that GA is also transformed in other reactions. Before catalytic tests, these two minerals were subjected to detailed instrumental analyses using the following methods: XRD, SEM/EDX, XRF and FTIR, which allowed to obtain their full morphological characteristics. During the catalytic tests, the influence of such relevant parameters on the GA transformations was determined: temperature from 80 to 150 °C, catalyst content from 5 to 15% by weight and the reaction time from 15 min to 24 h. The tests presented in the article were carried out under atmospheric pressure (in air) as well as without the use of a solvent. The optimal conditions for the transformations of GA were determined on the basis of its conversion and selectivities of transformation to the main products in the form of: beta-pinene (BP), 6,11-dimethyl-2,6,10-dodecatriene-1-ol (DC) and thumbergol (TH). The above products were formed with the highest selectivity, respectively: 100 mol%, 50 mol% and 52 mol%. The results of the syntheses showed that for GA the best transformation results were obtained at the temperature of 80 °C (for both tested catalysts), with the catalyst content of 1 wt % (for both tested catalysts) and for the reaction time of 1 h (for diatomite)) and 3 h (for alum).