Development of efficient catalysts for low temperature thermal oxidation of benzene

Abstract

Anthropogenic emissions of volatile organic compounds (VOCs) are demonstrated detrimental to human health and environment due to their elevated toxicity and to their participation in the formation of secondary pollutants. Those pollutants contribute to the increase of the incidence of several pathologies, including respiratory diseases and cancer, which cause millions of premature deaths every year. In China VOCs pollution was demonstrated to be the primary cause of the haze episodes and elevated level of PM often reported in recent years. The catalytic oxidation process is one of the technologies available for the removal of these hazardous pollutants from contaminated gases and represents a less energy intense option to the thermal incinerator process. However, the development of more efficient and resistant catalysts is necessary to increase the applicability of this technological option. For the first time this study assessed the applicability of diatomaceous earths as support material for the preparation of transition metal based catalysts using Mn, Co, Cu and Ce as active phases by incipient wetness deposition. Different diatomites (purified and non-treated) were fully characterized and their performances towards the oxidation of benzene in CO2 and water assessed. Further analyses were carried on prepared catalysts, which were also characterized by low temperature N2 adsorption-desorption, scanning electron microscopy, X-ray diffraction, inductively coupled plasma, temperature programmed reduction and temperature programmed desorption using H2 as probe molecule to justify the results observed during the activity tests. Prepared catalysts showed elevated activity towards the oxidation of benzene at low reaction temperature, the most active catalyst (Mn10Ce10) achieving over 90% conversion of benzene at reaction temperature of 200 °C. The high activity of prepared catalysts was attributed to the low crystallinity (with particles size ranging from 10 to 50 nm diameter) and high amounts of active sites. The effect of different metal combinations was assessed and although high activity was observed for all prepared catalysts, CoxMny, MnxCey and CuxCoy resulted more effective catalysts for the removal of benzene. None of the catalysts here described achieved 100% yield of CO2 and the formation of coke was observed on all prepared catalysts. However, Mn10Ce10 and Cu4Co15 resulted stable for over 50 h reaction time showing elevated stability. Overall, this study demonstrated that diatomaceous earths might represent a suitable support material for the preparation of catalysts, and Mn10Ce10 and Cu4Co15 emerged as the most effective catalysts prepared during this study.

Date of Award	10 Nov 2018
Original language	English
Awarding Institution	Univerisity of Nottingham
Supervisor	Jun He (Supervisor) & David Large (Supervisor)