Steam reforming of methanol over Li-doped Pt/m-ZrO2

The effect of Li loading on 2 %Pt/m-ZrO₂ catalyst was explored using temperature programmed, chemisorption, microscopic, spectroscopic, and micro-reactor testing methods. Up to 0.54 %Li loading, despite a small decrease in methanol conversion, the selectivity was altered remarkably from favoring unselective H₂-production pathways involving decarbonylation (300°C: 68.2 % CO, 30.3 % CO₂) to favoring the selective H₂-production pathway involving decarboxylation/dehydrogenation (300°C: 14.5 % CO, 85.2 % CO₂). In addition, the methanation selectivity decreased from 1.5 % to just 0.3 %. The primary advantage of Li over Na and K promoters, previously studied, is that Li provides the remarkable boost in selectivity without a significant loss in activity. At optimum loadings for selectivity, there was only a 13 % drop in conversion by adding 0.54 wt%Li, while more severe drops of 40 % and 55 % occurred for 2.5 wt% Na and 3.06 wt% K (atomic loadings close, 325 °C). CO₂-temperature programmed desorption and infrared spectroscopy (DRIFTS) showed that increased surface basicity caused by Li addition strains the formate intermediate to favor the dehydrogenation/decarboxylation route by strengthening -OOC bonding to the catalyst surface and weakening the C-H bond. Higher levels of Li tended to exacerbate Pt sintering (TEM), interact directly with Pt (XPS, DRIFTS of adsorbed CO), and inhibit CO₂ product desorption due to excessive basicity. The optimum formulation was found to be 0.54 wt% Li.