The hydrolysis of ruthenium alkoxide/titanium tetraethoxide mixtures to gels and powders containing 30-40 mol% Ru was investigated. Basic or neutral conditions led to powders consisting of 2-10 nm diameter crystalline RuO2 nanoparticles embedded in a matrix of crystalline (anatase) and amorphous TiO2. Acid hydrolysis conditions gave gels containing smaller, amorphous RuO2 nanoparticles (1-3 nm). In all samples the RuO2 nanoparticles tended to clump into aggregates up to 0.5 mu m across. Acid or neutral hydrolysis of ruthenium ethoxide gave samples which displayed lower surface Ru:Ti ratios as measured by XPS compared to the bulk (XRF), and also contained more low-valent Ru (as measured by XRF), probably due to incomplete hydrolysis of the precursors. These samples also contained more Ru metal after calcination (XRD). Calcination (450 degrees C) was accompanied by Ru-promoted combustion of organic material and led to crystalline (anatase) TiO2 and TixRu1-xO2 solid solution (rutile phase). (C) 2008 Elsevier B.V. All rights reserved.