H2 adsorption and direct methane conversion to methanol on Cu-exchanged zeolites

Lobo, Raul F.The adverse impact of atmospheric greenhouse gases and our heavy dependence on petroleum for materials and energy are an urgent call for sustainable methods in energy generation and chemical synthesis. Hydrogen fuel-cell vehicles are zero emission cars that run on compressed hydrogen stored in tanks at 70 MPa. Due to the volume and safety concerns, there is a need for a safer, lightweight and economical onboard hydrogen storage system with a target capacity of 5.5 wt.%. At the same time, efficient utilization of the increasingly important shale gas via methane conversion into valuable and more easily transportable liquid products in small-scales could help reduce our dependence on petroleum. Current methods for converting methane into chemicals involve synthesis gas production, economical only at large scale. Therefore, direct methane conversion into value added products such as methanol has been an important goal for the field of catalysis. There have been developments in selective methanol production using Cu-exchanged zeolites at mild conditions, however the low yields and the absence of a selective catalytic process leave a large room for research in this field. In this thesis, both challenges were investigated using Cu-exchanged small-pore zeolites with crystallographic and spectroscopic experiments focused on the material Cu-SSZ-13. H2 adsorption capacity that more than triple the capacity of the best metal-organic-frameworks (MOFs), reaching 0.05 wt.% were achieved at 30 °C and 1 atm using Cu(I)-SSZ-13 and Cu(I)-[B]-SSZ-13 with adsorption enthalpy around -20 kJ mol-1. The strong interaction of Cu(I)-SSZ-13 with H2 was also monitored using IR spectroscopy and neutron diffraction. In the second part of the thesis, Cu-exchanged SSZ-13, -SSZ-16 and SSZ-39 were tested for methanol formation and found to form methanol in quantities that are more than double the amounts produced by Cu-ZSM-5, the most investigated alternative. The active sites for methane activation on Cu-SSZ-13 and Cu-SSZ-39 were identified using optical spectroscopy and theory, while the optimum conditions for the formation of higher concentrations of the active site were reported. Finally, a new catalytic methanol production process was investigated using CH4, N2O, and steam on Cu-SSZ-13, and conditions for achieving higher selectivity were suggested.University of Delaware, Department of Chemical and Biomolecular EngineeringPh.D