A General Strategy for the Design of New Solid Catalysts for Environmentally Benign Conversions: Solid Catalysts for Benign Conversions

Dehydration of fructose over thiol- and sulfonic- modified alumina in a continuous reactor for 5-HMF production: Study of catalyst stability by NMR

In the present study, the synthesis of an organic group-modified alumina by the sol-gel method is proposed. This material has shown to have an enhanced catalytic performance with grafted organic groups and showed an improved stability. The prepared material has shown to have several O - H groups and an enhanced surface acidity. The alumina acidity was improved by incorporating thiol groups by grafting method, which promotes the tautomerization of fructose to its furanose form. Furthermore, the grafting of sulfonic groups catalyzes its dehydration. The modified alumina was thermally treated up to 200 °C to improve the functional groups stability. After, this modified material was packed into a continuous reactor system, designed and built by this group, to obtain 5-hydroxymethylfurfural (5-HMF) from fructose dissolved in a single-phase solution of tetrahydrofuran (THF) and H2O (4:1 w/w). The catalytic activity of this material was evaluated by the reaction of fructose dehydration at different reaction temperatures (60, 70, 80 and 90 °C). Fructose conversion and selectivity toward 5-HMF were determined by high performance liquid chromatography (HPLC), obtaining 95% and 73% respectively for the highest temperature. The catalyst showed an efficient stability after 24 hours in continuous flow at 70 °C. The loss of sulfur content was 15%, but the fructose conversion yield and the selectivity to 5-HMF after 24 hours of continuous reaction did not undergo significant changes (less than 5%). The nuclear magnetic resonance (NMR) tests confirmed the presence of the thiol and sulfonic groups before and after 24 hours of reaction, as well as the conservation of the same structure, demonstrating the efficient catalytic performance of the material. The catalysts were characterized by nitrogen adsorption/desorption, X-ray diffraction and infrared (IR) spectroscopy. Also, before and after use by utilizing elemental analysis and  1 H - 13 C cross-polarization magic-angle spinning (CPMAS) and dynamic-nuclear polarization (DNP)-enhanced  1 H - 13 C and  1 H - 29 Si CPMAS as well as directly excited  29 Si magic-angle spinning (MAS) NMR methods in solid-state.

Providing sustainable catalytic solutions for a rapidly changing world: a summary and recommendations for urgent future action

In addition to summarizing the main thrusts of each paper presented at this Discussion, other urgent issues involving the role (and characterization) of new catalysts for eliminating oxides of nitrogen, for using CO₂ liberated from steel mills, for fuel cells and the need for rapid decarbonization of fossil fuels are outlined.This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'.

The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts

The concept of single-site heterogeneous catalysis, herein defined and extensively illustrated, offers a strategy for the design of new solid catalysts. By capitalizing on the opportunities presented by nanoporous materials to assemble a wide range of new, well-defined, catalytically active centres, it is possible to bring about numerous environmentally benign processes that can replace traditional methods of chemical production. The latter often employs aggressive, corrosive or hazardous reagents. By using both microporous (less than 20 Å diameter) and mesoporous solids (20–500 Å diameter), abundant scope exists for the construction and application of shape-selective, regio-selective and enantioselective catalysts.

Tin-containing silicates: structure–activity relations

The selective conversion of biomass-derived substrates is one of the major challenges facing the chemical industry. Recently, stannosilicates have been employed as highly active and selective Lewis acid catalysts for a number of industrially relevant reactions. In the present work, four different stannosilicates have been investigated: Sn-BEA, Sn-MFI, Sn-MCM-41 and Sn-SBA-15. When comparing the properties of tin sites in the structures, substantial differences are observed. Sn-beta displays the highest Lewis acid strength, as measured by probe molecule studies using infrared spectroscopy, which gives it a significantly higher activity at low temperatures than the other structures investigated. Furthermore, the increased acid strength translates into large differences in selectivity between the catalysts, thus demonstrating the influence of the structure on the active site, and pointing the way forward for tailoring the active site to the desired reaction.