Nitrous oxide decomposition and low temperature parahydrogen enrichment on pure and doped rutile

Doping with 0.1 mol % Cr2O3, Fe2O3, NiO, Nb2O5 or WO3 has little effect on the catalytic properties of rutile for the decomposition of nitrous oxide in the temperature range 450–590°C. For all six catalysts, first-order kinetics with respect to initial nitrous oxide pressure were obeyed. Relatively small differences in the activation energies were observed, but an apparent compensation effect resulted in the absolute rates at 550°C and 1.33 × 104 N m–2 lying between 1.2 and 2.2 × 1012 molecules cm–2 s–1. Parahydrogen enrichment has been investigated at 77 and 90 K over the pressure range 1.33 × 102 to 2.66 × 104 N m–2 on the six catalysts used in nitrous oxide decomposition. The reaction proceeds by the paramagnetic vibrational mechanism on a small active fraction of the oxide surface. Results obtained for other samples of doped rutile, and analytical measurements on progressively dissolved material, show the existence of a surface excess concentration of dopent both at a nominal concentration of 0.1 mol % and at 100 p.p.m. Inhomogeneity in doped titanium dioxide, which has not been reported previously, is of importance in the catalytic properties of such material.