Surface acidity of niobium phosphate and steam reforming of dimethoxymethane over CuZnO/Al_2O_3-NbP complex catalysts

摘要

Dimethoxymethane (DMM) is nontoxic and of high hydrogen content and may be used as a H_2 storage material for small H_2 sources. Steam reforming of DMM requires a bifunctional catalyst composed of an acidic component and a traditional copper catalyst, on which DMM is hydrolyzed on the acidic sites to methanol and formaldehyde, which are then further reformed to H_2 and CO_2 on metallic copper sites. In this work, samples of niobium phosphate with high surface areas were synthesized, characterized, and tested for the hydrolysis of DMM and used as acidic components for the reforming of DMM to produce H_2. The structure and surface areas of these samples were characterized, and the activity for the hydrolysis of DMM was correlated with the surface acidities. It was found that all of the niobium phosphate samples exhibited high activity for the hydrolysis of DMM. The one with a high surface area (394 m~2/g) was highly acidic with mainly Br0nsted acid sites and thus was the most active for the hydrolysis of DMM among the niobium samples studied in this work. Mixing the niobium phosphate with CuZnO/Al_2O_3 did not affect the activity of CuZnO/Al_2O_3 for the reforming of methanol. The activity and selectivity to H_2 were low for the steam reforming of DMM over traditional CuZnO/Al_2O_3 alone. Mechanically mixing niobium phosphate with CuZnO/Al_2O_3 greatly enhanced the conversion of DMM (e.g., 100% at 493 K) with high selectivity to H_2. This indicates that niobium phosphate is an effective acidic component for the hydrolysis of DMM and can be used with CuZnO/Al_2O_3 for reforming DMM to produce H_2.