NH3-TPD characterization is done to study the acid strength of catalyst samples. Fig. 3 illustrates the acid sites strength on as-prepared catalysts, reduced at various temperatures. The desorption peaks at low and high temperatures could be assigned to desorption of NH3from the medium and strong acid sites, respectively. The NH3-TPD results indicate that the acid strength and the acid concentration of as-synthesized catalysts rapidly decrease with the increase in the reduction temperature. The peaks at 393 369 and 323◦C are assigned to the desorption of NH3on the medium Lewis acid sites of TiO2; whereas, the strong and conspicuous peak at 458◦C is ascribed to desorption of NH3on the strong Lewis acid sites of the TiO2NWs support. The Lewis acidity is responsible for the hydrolysis of cellobiose. The lump acid concentration, calculated from the analysis of NH3-TPD, is 476 mol g−1for TiO2NWs, and 387.8, 354.54 and 251.7 mol g−1for Au–Cu/TiO2NWs reduced at 300, 500 and 700◦C, respectively. It is worth stat-ing that, although the sample reduced at 700◦C exhibits the lowest acid strength, gluconic acid selectivity is the highest over this particular catalyst, indicating that the hydrolysis of cellobiose is not the limiting step. It is anticipated that the decrease in acid amount with an increase in the reduction temperature could be related to the progressive dehydroxylation of TiO2NWs surface