(344a) Water Is the Oxygen Source for Methanol Produced in Partial Oxidation of Methane in a Flow Reactor over Cu-SSZ-13

The direct oxidation of methane to methanol represents a grand challenge problem. Copper-containing zeolites have attracted attention recently due to their high selectivity to methanol under moderate reaction conditions. The partial oxidation of methane to methanol can be achieved via chemical looping or continuous processes using molecular oxygen as an oxidant and water as an extracting solvent. It has been long considered that water is only necessary for extraction of surface bound methanol while being kinetically inconsequential. However, the current work demonstrates that water can be used as a “soft” oxidant for methane oxidation in a continuous partial oxidation of methane reaction. The continuous partial oxidation of methane to methanol over Cu-SSZ-13 with water in the absence of molecular oxygen showed that active copper site motifs under steady-state conditions can in fact be formed and maintained without apparent deactivation for over 30 hours. The operando Fourier transform infrared spectroscopy (FTIR) measurement technique was applied to confirm the source of the oxygen in the methanol obtained. The isotopically labelled CH₃¹⁸OH and regular CH₃¹⁶OH have two distinct C-O stretching modes at 1007 cm^-1 and 1033 cm^-1, respectively. The evidence that the water vapor present in the continuous partial oxidation of methane is the main source of the oxygen atom in the methanol synthesis, was obtained for reactions ran with 18O-labelled water. The time-resolved IR spectra of C-O stretching mode has shown formation of 1007 cm^-1 peak and it remained constant for the duration of the reaction. This result is a very strong proof that the oxygen in the methanol under long time steady-state conditions in fact comes from the water fed into the system.