A composite catalyst consisting of Nb2O5 and platinized TiO2 particles is found to initiate up-hill chemical reactions via a low-energy multiphoton process involving step-wise transition of electrons across the traps in Nb2O5 to the conduction band of Nb2O5 and then to the conduction band of TiO2. (C) 2000 Elsevier Science B.V. All rights reserved.