Air pollution arising from oxides of nitrogen (NOx) as a result of combustion has increasingly been recognised as a problem for the environment and human health. Oxides of nitrogen (NOx) are known precursor to formation of for ozone layer depletion, acid rain photo-chemical smog. Due to adverse effects of NOx, it is classified as one of the criteria air pollutants. Basically, the combustion flue gas contains nitric oxide (NO) which immediately oxidises to form nitrogen dioxide (NO2). There are three different ways to reduce NO emissions from combustion: (1) Use low nitrogen fuels like liquid fuels or natural gas (2) Reduce the formation of NO during combustion by modifying process parameters or design of combustion chamber and (3) Post combustion technologies to reduce NO emission from the flue gas. Among all the technologies, selective catalytic reduction of NO using ammonia is a commercial technology to remove NO from combustion flue gas. Due to some disadvantages of this process like ammonia storage, oxidation of ammonia and deactivation of catalysts, research focus has been drawn toward using hydrocarbons (HC) and carbon monoxide (CO) as reducing agent. There are number of reported studies on the NO reduction with CO and HC using various supported and unsupported metal oxides or noble metal catalysts.
This project focuses on the use mesoporous material supported catalysts for the reduction of NO with CO. Mesoporous materials provide high surface area, pore volume and organised pore structure for the homogeneous dispersion of metal particles which affects catalytic activity. The mesoporous silica (SiO2), alumina (Al2O3) and manganese oxide (MnOx) supported copper oxide (CuO) catalysts have been reported in this study.
Copper oxide supported on mesoporous SBA-15 and MCM-41 showed higher catalytic activity compared to CuO/MCM-48 and CuO/KIT-6. The pore structure of the silica material influences catalytic activity for NO-CO reaction. The conversion of NO increased with increase in the CuO loading up to certain value when reaction was carried out over CuO/SBA-15.
Copper oxide supported on mesoporous alumina for NO-CO reaction reported in this study. It is observed that the activity of the CuO/mesoporous alumina was affected by calcination temperature of mesoporous alumina and CuO loading. Presence of bulk and surface copper species found to be responsible for the higher catalytic activity for NO-CO reaction. Mesoporous manganese oxide (MnOx) and CuO supported on mesoporous MnOx showed promising results for reduction of NO with CO. Mesoporous manganese oxide showed maximum 70% NO conversion and it increased after loading CuO on the MnOx. The synergetic effect of both metal oxides played important role in the catalytic activity.
The catalytic activity of the other metals oxides (NiO, RuO2, Fe2O3, Co3O4, CuO and Ag2O) supported on MCM-41 for NO-CO reaction compared in this study. The catalysts were synthesised by co-precipitation method to enhance the dispersion of metal particles in the pores of MCM-41. Among all these catalysts, RuO2/MCM-41 showed highest activity at lower temperature. It was concluded that the onset reaction temperature was influenced by metal oxygen bond strength. The reaction kinetics of the NO-CO reaction studied on three selected catalyst with different properties. It was observed that the kinetic parameters were dependent on the catalyst and support properties. The reaction mechanism of the NO-CO reaction proposed from the obtained kinetic parameters. The catalysts used in this study were also thoroughly characterised by different physicochemical techniques and reported in this thesis.