Defect chemistry in ruthenium-supported tin dioxide: a spectromagnetic approach

The reactivity towards CO and air of SnO(2) defects, singly and doubly ionized oxygen vacancies (V(o)(.) V(o)(..)), bivalent tin centers, was studied in ruthenium-supported tin oxide (Ru/SnO(2)), and compared with that in pure SnO(2). Electron paramagnetic resonance and X-ray photoelectron spectroscopy studios demonstrated that CO treatment produces V(o)(.) and V(o)(..) defects in SnO(2), some V(o)(.) transferring their electrons to Sn(4+) centers; instead in Ru/SnO(2), some V(o)(.) defects transferred their electrons to Ru(n+) centers (n=0,1,2,3) and no one bivalent tin center was observed. When contacted with air, pure SnO(2) transferred a part of the electrons of V(o)(.) and of bivalent tin centers to O(2), instead Ru/SnO(2) emptied all V(o)(.) defects transferring the electrons from V(o)(.) to ruthenium and to O(2). The via ruthenium transfer increases the number of electrons exchanged between SnO(2) and the surrounding atmosphere and gave a rationale for the higher sensitivity towards CO displayed by transition metal-doped SnO(2) with respect to pure SnO(2). (C) 2000 Elsevier Science Ltd. All rights reserved.