Abundant natural gas, containing mostly methane (CH4), provides a source of energy as well as carbon and hydrogen for chemicals production. A large amount of natural gas, however, is wasted through flaring at oil production sites due to the lack of transportation infrastructure. Converting natural gas to methanol (CH3OH), which is a liquid, would provide a beneficial route towards increased utilisation of natural gas as methanol transportation is rather facile. In fact, methanol is one of the important chemical feedstocks in the chemical industry. In the longer perspective biomethane produced from biomass would realise a green methanol production with low carbon footprint.
This work focuses on catalysts for once-through conversion of methane to methanol at ambient pressure and low temperature. In this, one faces great challenges due to that both methane and oxygen (O2) must be activated while formed methanol should be preserved. Breaking the chemical bonds in methane and oxygen, even when using a catalyst, requires considerable energy input (temperature) that often ruins the production of methanol as it easily decomposes. Inspired by the structure and functionality of natural enzymes that convert methane to methanol under ambient conditions, metal containing zeolites have been considered to be appropriate inorganic catalyst counterparts. One great challenge, however, is methanol desorption from the metal containing zeolites, which is realised through an extraction step.
This thesis reports studies on different copper containing zeolites (Cu-zeolites) for partial methane oxidation to methanol. Particular attention is paid to facilitate the liberation of methanol from the Cu-zeolites by desorption experiments. The results suggest that the zeolite acidity plays an important role for desorption of methanol. With this as point of departure, the acidity of zeolites was tuned in an attempt to govern the methanol desorption. Several modified materials were successfully synthesised of which one showed promising results in methane oxidation experiments.