Different sulfated catalysts including SO 4 /TiO 2 −SiO 2 , SO 4 /Ti-SBA-15, SO 4 /ZrO 2 , SO 4 /AC, and SO 4 /SiO 2 were tested in fructose dehydration to 5-hydroxymethylfurfural (HMF). Reactions were carried out in dimethyl sulfoxide (DMSO) at 110°C. Characterization results indicated that no sulfur leaching was observed from SO 4 /ZrO 2 , SO 4 /TiO 2 −SiO 2 , and SO 4 /Ti-SBA-15 catalysts in the reaction tests. The SO 4 /TiO 2 −SiO 2 catalyst had a high amount of strong acid sites and the highest amount of Bronsted sites. The highest selectivity to HMF at high conversion, that is, 89% selectivity at 77% fructose conversion was obtained over this catalyst. It preserved its activity after four times reuse. ■ INTRODUCTIONDiminishing fossil fuel reserves and CO 2 emission problems force people to find alternative and sustainable resources to produce valuable chemicals. Production of these chemicals from biomass is an environmentally friendly process compared to a petroleum based process. 5-Hydroxymethylfurfural (HMF) is one of the key intermediates in order to convert the biomass to valuable chemicals such as polymers, biofuels, and bulk chemicals. 1 The most effective way of producing HMF is by carbohydrate conversion, especially dehydration of fructose.Fructose dehydration reaction occurs on the acid sites of the catalyst. Acid concentration, type of acid sites, and acid strength of the catalyst affect the product distribution significantly. 2−4 It is reported that fructose conversion to intermediates takes place on the Lewis sites, whereas Bronsted sites are responsible for the HMF formation from these intermediates. 5 Various acid catalysts including homogeneous (ionic liquids, mineral and organic acids) and heterogeneous types have been investigated. Because of the product contamination and recovery problems, heterogeneous catalysts are generally preferred. Wide ranges of heterogeneous catalysts (e.g., resins, metal sulfates, metal phosphates, heteropolyacids, zeolites, niobic acid based catalysts) have been tested. 3,6−15 However, no satisfactory yields have been achieved yet. Some of the catalysts have low stabilities due to leaching and some of them are not selective and promote side product formation such as formic acid and levulinic acid. Therefore, there are still studies pursued to find a stable, active, selective, and cheap heterogeneous catalyst for fructose dehydration to HMF.Sulfur ions and sulfate groups create Bronsted and strong acid sites when loaded on a support, such as iron oxide, alumina, titania, and zirconia. They were very active in fructose dehydration. 7,17 However, they leached during the reaction in different solvents. Solvent type also affects HMF yield. Different types of solvents from environmentally benign alcohols and water to the high-boiling-point polar aprotic solvents (dimethyl sulfoxide (DMSO) and dimethylamide (DMA)) have been investigated. High yields of HMF have been achieved by using high-boiling-point solvents such as DMSO and DMA. 9 Zirconia is known as ...

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H-ZSM-5 was modified by silylation [tetraethylorthosilicate (TEOS) and triaminopropyltriethoxysilane], alkali (NaOH), acid (HCl) and ammoniumhexafluorosilicate (AHFS) treatments. The parent and modified zeolite forms were tested in n-butene isomerization. Modifications affected total acidities, the strength of the acid sites, pore sizes and surface areas of the H-ZSM-5 differently. The modifications decreased the conversion obtained by the parent catalyst. TEOS and alkali modifications did not promote formation of isobutene. Pre-alkali treatment before acid treatment increased selectivity to isobutene from 56.0 to 66.7 %, while conversion changed a little, it dropped from 52 to 50 %. AHFS modification provided the highest enhancement in selectivity to isobutene (87.5 %) for which n-butene conversion was dropped by about 10 % compared to H-ZSM-5. This was attributed to a slight modification of the pore size and to the reduction in strong and weak acid sites and generation of new Lewis acid sites.

H-ZSM5 and H-Ferrierite acidities were modified by chemical liquid deposition using tetraethylorthosilicate (TEOS), silicontetratchloride (SiCl 4 ) and triaminopropyltriethoxysilane (3-APTES). All depositions were carried out at room temperature for deposition times of 0.5 and 1 h. Reaction tests were performed in a tubular quartz fixed bed reactor at 375• C for weight hour space velocities of 22 h-1. Surface area and pore volume of the catalysts were decreased upon modifications. The least modification of acidity was achieved by TEOS. However, SiCl 4 and 3-APTES deposition modification strongly decreased the number of Bronsted and Lewis acid sites. As the effect of the modification increased, total acidity of the SiCl 4 modified catalyst decreased. The catalysts were tested in isomerization of n-butene. Modification decreased the activity of the catalysts, but improvement in selectivity was observed with TEOS deposition. TEOS deposition increased the selectivity of the catalysts; for synthesized H-ZSM5 from 57.95 to 63.74 percent, for commercial H-ZSM5-C from 26.78 to 32.52 percent, and for H-FER from 63.06 to 81.23 percent. However, modification with SiCl 4 and 3-APTES decreased both conversion and selectivity of the parent catalysts.