MCM-41 is a mesoporous silica molecular sieve with very high surface area, arrow pore size distributions and simple pore size engineering which makes it potential catalyst support for the eco-friendly CO2 conversion into carbamates using alkyl halides and amines. Despite all the merits, MCM-41 suffers a lack of hydrothermal stability. The highly ordered pore-network of MCM-41 collapses when MCM-41 comes in contact with moisture. In this work, highly ordered MCM-41 having high hydrothermal stability was prepared using tetraalkylammonium bromide salts and post-synthesis hydrothermal treatment. Powder X-ray diffraction results confirmed the presence of a highly ordered characteristic hexagonal MCM-41 structure. Nitrogen physisorption analysis revealed an unprecedented ultra-high specific surface area of 3000 m2g-1, calculated using the Brunauer-Emmett-Teller (BET) method and a very narrow pore size distributions (2.6-3.7nm) calculated by the Barrett-Joyner-Halenda (BJH) model. The pore-wall thickness of MCM-41 was found to be 2 nm. The MCM-41 material synthesised exhibited high hydrothermal stability by retaining its structure after boiling in water for 48 hours which is the highest hydrothermal stability reported to date. The most hydrothermally stable MCM-41 samples reported in the literature showed a structural decline after 12-24 hours boiling in water. The ultrahigh surface area MCM-41 thus prepared was impregnated with vanadium using the wet impregnation technique. The wide-angle X-ray diffractograms revealed an extremely uniform dispersion of V species without any degradation of MCM-41 structure. In future, the vanadium impregnated MCM-41 synthesised in this research can potentially be employed as a catalyst for the conversion of CO2 into carbamates and many other useful chemicals. Due to its high surface area, MCM-41 prepared in this work can also be impregnated with other potential catalysts such as ammines and metal oxides associated with CO2 conversions. MCM-41 can also be exploited for carbon capture and storage.
|Date of Award||18 Oct 2019|
|Supervisor||Joseph McGinnis (Supervisor) & Maria Olea (Supervisor)|