Bifunctional SO₄/ZrO₂catalysts for 5-hydroxymethylfufural (5-HMF) production from glucose

Abstract

The telescopic conversion of glucose to fructose and then 5-hydroxymethylfurfural (5-HMF), the latter a potential, bio-derived platform chemical feedstock, has been explored over a family of bifunctional sulfated zirconia catalysts possessing tuneable acid-base properties. Characterisation by acid-base titration, XPS, XRD and Raman reveal that submonolayer SO 4 coverages offer the ideal balance of basic 10 and Lewis/Brönsted acid sites required to respectively isomerise glucose to fructose, and subsequently dehydrate fructose to 5-HMF. A constant acid site normalised turnover frequency is observed for fructose dehydration to 5-HMF, confirming a common Brönsted acid site is responsible for this transformation. 65 110 stabilise. pH measurements on aqueous catalyst suspensions were performed by adding 0.1g of each catalyst to 20 ml of deionized water and stirring at room temperature. After 30 min the solution pH was measured using a Jenway 3305 pH meter.

Acidity-Reactivity Relationships in Catalytic Esterification over Ammonium Sulfate-Derived Sulfated Zirconia

“…This chemical shift is attributed to the electron-withdrawing effect of sulfate groups, and hence an increase in initial state charge (and Lewis acidity) in Zr 4+ species. The S 2p 3/2 binding energy was around 169-170 eV for all samples ( Figure S2a), consistent with SO 4 formation [1,7], and, as previously reported, exhibited a small increase with S loading (from 169.0 → 169.4 eV) previously attributed to the genesis of co-existing bidentate and monodentate SO 4 species due to lateral interactions on the crowded surface, reducing the extent of charge-withdrawal from the zirconia substrate. O 1s spectra ( Figure S2b) show that sulfation induces a similar small shift to higher binding energy in the surface oxygen species from 529.7 → 530.3 eV ( Figure S2), accompanied by the growth of a second, high binding chemical state at 531.65 eV attributed to surface hydroxyls.…”

“…A gradual weakening of the t-ZrO 2 reflections was observed for S loadings ≥3.10 wt %, which has previously been attributed to the formation of amorphous, bulk Zr(SO 4 ) 2 [20]. It is noteworthy that sulfation by sulfuric acid was observed to cause a complete loss of crystallinity for S loadings of 3 wt % [1], highlighting the benefits of (NH 4 ) 2 SO 4 as a more mild sulfating agent that preserves structural order.…”

“…These properties have found catalytic application in, for example, the isomerization of glucose to fructose [1], and the synthesis of dimethyl carbonate [2]. The chemical functionalization of zirconia surfaces with sulfate ions to generate SO 4 /ZrO 2 (SZ) solid acid catalysts has attracted significant industrial and academic interest.…”

“…The chemical functionalization of zirconia surfaces with sulfate ions to generate SO 4 /ZrO 2 (SZ) solid acid catalysts has attracted significant industrial and academic interest. Early research focused on exploiting the strong (even super-) acidic properties of SZ for gas phase cracking and isomerization of hydrocarbons; however, catalytic applications have expanded in recent years to include liquid phase green chemical processes such as free fatty acid esterification and triglyceride transesterification [3,4], Friedel-Craft alkylation [5], alkane and terpene isomerization [6,7], sorbitol dehydration [8], and glucose conversion to HMF [1]. The promising performance of SZ for these catalytic transformations is mainly attributed to its strong solid acidity and good thermal stability, which are strongly influenced by the sulfation method, sulfur content, and calcination temperature [9].…”

Fructose Dehydration to 5-Hydroxymethylfurfural over Sulfated TiO2–SiO2, Ti-SBA-15, ZrO2, SiO2, and Activated Carbon Catalysts

“…23 However, the monoclinic phases were found to favor the side products formation. 24,27 Selectivities obtained for SO 4 /AC and SO 4 /SiO 2 catalysts include the contribution from leached sulfur. Thus, the results cannot be related to their acidity only.…”