Catalytic glucose and fructose conversions with TiO 2 and ZrO 2 in water at 473 K: Relationship between reactivity and acid–base property determined by TPD measurement Masaru Watanabe, Yuichi Aizawa, Toru Iida, Ryo Nishimura, Hiroshi Inomata * Research Centerof Supercritical Fluid Technology, Tohoku University, 6-6-11-403 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Received 23 June 2005; received in revised form 26 July 2005; accepted 1 August 2005 Available online 19 September 2005 Abstract The effects of TiO 2 (anatase TiO 2 or rutile TiO 2 ) and ZrO 2 (monoclinic/tetragonal mixture ZrO 2 ) on glucose and fructose reactions were examined in hot-compressed water at 473 K with a batch type reactor. Rutile TiO 2 (r-TiO 2 ) is inactive during glucose reactions. A monoclinic/ tetragonal mixture of ZrO 2 (m/c-ZrO 2 ) was the basic catalyst for the reaction at this temperature. Anatase TiO 2 (a-TiO 2 ) showed both acidity and basicity during the reactions. In order to understand the catalytic activity of a-TiO 2 , r-TiO 2 , and m/c-ZrO 2 , we measured the acidity and basicity by means of NH 3 - and CO 2 -TPD, respectively. The TPD analysis showed us that the amount of acid (670 mmol/g) and base (550 mmol/g) sites on m/c-ZrO 2 were the highest among these three catalysts, while the density of acid site (17 mmol/m 2 ) and that of basic site (9 mmol/m 2 ) of the a-TiO 2 were the highest. Such the acidity and basicity analyses suggested that the amount of basicity was the key factor for the isomerization while the density of acidity and basicity was important for the HMF formation from glucose. # 2005 Elsevier B.V. All rights reserved. Keywords: Glucose; TiO 2 ; ZrO 2 ; Acidity; Basicity; TPD; BET 1. Introduction A high-speed and highly selective process for glucose conversion will strongly be demanded within a decade because glucose is the monomer unit of cellulose and will be one of the most important resources. In order to develop the process, scientists favor hot-compressed water including hydrothermal and supercritical water (SCW) conditions for the following reasons: (i) water is a suitable solvent on the earth, (ii) ionic and radical reaction can be selected by controlling pressure and temperature [1], (iii) the component of woody biomass is fragmented by hot-compressed water [2] and (iv) cellulose is quickly hydrolyzed to oligomer and monomer units in hot-compressed water [3]. Glucose conversion in hot-compressed water has been reported with and without additive at hydrothermal and supercritical regions [4–15]. The primary reactions of glucose can be roughly classified into the follow three reactions (see Fig. 1): dehydration, isomerization, and retro- aldol condensation. The primary products of these reactions are fructose through isomerization, 1,6-anhydroglucose (AHG) through dehydration of glucose, 5-hydroxymethyl- 2-furaldehyde (HMF) mainly through dehydration of fructose, and small fragments such as glycolaldehyde and dihydroxyacetone, etc., through retro-aldol condensation. The control of these reactions is quite important to develop a biomass refinery process in hot-compressed water. Kabye- mela et al. [5] revealed that the rate of glucose isomerization into fructose was significantly higher than that of fructose isomerization into glucose in supercritical water. At a lower temperature, a base catalyst promotes the glucose isomer- ization into fructose in water (e.g. [9,15]). Sasaki et al. [10] reported that the retro-aldol condensation selectively proceeded at higher temperatures (above 673 K) and lower pressure (below 25 MPa). At a low temperature, the retro- www.elsevier.com/locate/apcata Applied Catalysis A: General 295 (2005) 150–156 * Corresponding author. Tel.: +81 22 795 7283; fax: +81 22 795 7282. E-mail address: inomata@scf.che.tohoku.ac.jp (H. Inomata). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.08.007