Pedro Maireles-Torres

Furfural: a renewable and versatile platform molecule for the synthesis of chemicals and fuels

The production of future transportation fuels and chemicals requires the deployment of new catalytic processes that transform biomass into valuable products under competitive conditions. Furfural has been identified as one of the most promising chemical platforms directly derived from biomass. With an annual production close to 300 kTon, furfural is currently a commodity chemical, and the technology for its production is largely established. The aim of this review is to discuss the most relevant chemical routes for converting furfural to chemicals, biofuels, and additives. This review focuses not only on industrially produced chemicals derived from furfural, but also on other not yet commercialised products that have a high potential for commercialisation as commodities. Other chemicals that are currently produced from oil but can also be derived from furfural are also reviewed. The chemical and engineering aspects such as the reaction conditions and mechanisms, as well as the main achievements and the challenges still to come in the pursuit of advancing the furfural-based industry, are highlighted.

Textural and structural properties and surface acidity characterization of mesoporous silica-zirconia molecular sieves

Homogeneous mesoporous zirconium-containing MCM-41 type silica were prepared by supramolecular templating and their textural and structural properties were studied using powder X-ray diffraction, N2 porosimetry, atomic force microscopy, EXAFS, XPS, and UV–VIS–NIR diffuse reflectance spectroscopy. Their acid properties were also studied by using IR spectroscopy and by the use of catalytic tests such as the decomposition of isopropanol and the isomerization of 1-butene. The materials prepared show a good degree of crystallinity with a regular ordering of the pores into a hexagonal arrangement and high thermal stability. The specific surface area of the prepared materials decreases as the zirconium content rises. Zirconium atoms are in coordination 7 to 8 and located at the surface of the pores such that a high proportion of the oxygen atoms bonded to zirconium corresponds to surface non-condensed oxygen atoms. Both facts are responsible for the acid properties of the solids that show weak Bronsted and medium strong Lewis acidity.

Surfactant‐Assisted Synthesis of a Mesoporous Form of Zirconium Phosphate with Acidic Properties

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Catalytic behavior of vanadium-containing mesoporous silicas in the oxidative dehydrogenation of propane

Three series of vanadium-containing silica catalysts (2–7.6 wt% V) have been prepared by varying the synthesis method. In all cases, conversion values in the oxidative dehydrogenation of propane increase with the temperature, vanadium loading and reducibility. For impregnated and anchored catalysts, a relationship between the selectivity towards propene and the effective acidity, as determined in the dehydration of 2-propanol, can be established.

Dehydration of Xylose to Furfural over MCM-41-Supported Niobium-Oxide Catalysts

A series of silica-based MCM-41-supported niobium-oxide catalysts are prepared, characterized by using XRD, N2 adsorption-desorption, X-ray photoelectron spectroscopy, Raman spectroscopy, and pyridine adsorption coupled to FTIR spectroscopy, and tested for the dehydration of D-xylose to furfural. Under the operating conditions used all materials are active in the dehydration of xylose to furfural (excluding the MCM-41 silica support). The xylose conversion increases with increasing Nb2 O5 content. At a loading of 16 wt % Nb2 O5 , 74.5 % conversion and a furfural yield of 36.5 % is achieved at 170 °C, after 180 min reaction time. Moreover, xylose conversion and furfural yield increase with the reaction time and temperature, attaining 82.8 and 46.2 %, respectively, at 190 °C and after 100 min reaction time. Notably, the presence of NaCl in the reaction medium further increases the furfural yield (59.9 % at 170 °C after 180 min reaction time). Moreover, catalyst reutilization is demonstrated by performing at least three runs with no loss of catalytic activity and without the requirement for an intermediate regeneration step. No significant niobium leaching is observed, and a relationship between the structure of the catalyst and the activity is proposed.

Catalytic behaviour of chromium supported mesoporous MCM-41 silica in the oxidative dehydrogenation of propane

A series of chromium supported mesoporous MCM‐41 silica catalysts (0.5–6 wt% Cr) were prepared and tested in the oxidative dehydrogenation of propane between 350 and 550°C. The catalytic activity, observed at temperatures as low as 350 °C, can be well explained on the basis of the existence of highly dispersed and reducible chromium species.

Nickel-impregnated zirconium-doped mesoporous molecular sieves as catalysts for the hydrogenation and ring-opening of tetralin

Catalysts based on nickel supported on zirconium-doped mesoporous silica, with nickel loadings of 15 and 30 wt.%, have been prepared, characterized and tested in the hydrogenation of tetralin at high hydrogen pressures (6.0 MPa). The zirconium-doped mesoporous silica, used as support, is revealed as appropriate for attaining a high loading of metallic nickel with a suitable degree of dispersion, although the large metallic particles are located on the external surface of the support. These catalysts are very active in the hydrogenation of tetralin at 350 ◦ C, specially that with the highest nickel content, with no deactivation by coke deposition. Concomitantly, the mild acidic nature of these catalysts favor the ring-opening of the tetralin molecules, up to 28% of cracking products at moderate temperatures are detected and the amount of volatile compounds is almost negligible under these experimental conditions.

Liquid phase acetophenone hydrogenation on Ru/Cr/B catalysts supported on silica

The liquid phase hydrogenation of acetophenone was studied over a series of silica supported bimetallic catalysts with various Ru/Cr atomic ratios. The catalysts were prepared by reduction of the metal salts with NaBH4 aqueous solutions and were characterised by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) (ESCA). The hydrogenation reaction was carried out in batch at a hydrogen pressure of 9 bar. The selectivity towards reduction of the carbonyl function increases with the increasing amount of Cr ions added.

Proton conductivity of mesoporous MCM type of zirconium and titanium phosphates

Abstract A family of novel mesoporous zirconium(IV) and titanium(IV) phosphate materials has been prepared by sol-gel synthesis in the presence of cetyltrimethylammonium bromide, a structure-directing cationic surfactant. The solids obtained after removal of the surfactant by acid-ethanol extraction or by calcination have high BET surface areas of 240–330 m2g−1 and a narrow pore size distribution in the mesopore range. AC conductivity measurements of these solids were carried out by impedance spectroscopy. The data indicate that two electric relaxation processes are present; one at low frequency, associated with the grain boundary and one at higher frequency related to a relaxation within the pores. Although a partial contribution of electronic conduction cannot be excluded, the major contribution comes from proton mobility along the channels.

Porous chromia-pillared α-zirconium phosphate materials prepared via colloid methods

The reaction of Cr(CH3CO2)3[Cr(OAc)3] with colloidal n-propylammonium α-zirconium phosphate and subsequent calcination of the products have been investigated. Depending on [Cr(OAc)3] : [initial phosphate] ratios and Cr3+ concentrations, a series of polyhydroxy acetato-Cr3+ intercalated precursor materials can be obtained, in which topotactic interface reactions have occurred to give materials with interlayer distances (d002) ranging from 13.0 to 39.0 A. These precursors show higher layer expansions than the analogous pillared clays (PILCS; d001= 16.8–27.6 A). A model invoking ordered in situ polymerisation of the Cr(OAc)3 on the phosphate surfaces is put forward.Calcination of these precursors under N2(400 °C) leads to a series of chromia-pillared materials in which the interlayers do not collapse to a single (much lower) value, as found previously for most PILCS, but instead provide a wide range of interlayer distances (10–27 A). These correspond to free heights of 3.5–20.5 A, the widest ranging and highest yet found for such materials. These nanoscale oxide-pillared materials have N2 surface areas (B.E.T., 77 K) of 250–330 m2 g–1, with pore radii (cylindrical pore method) ranging from 8.5 to 13.8 A, and very narrow pore-size distributions. Calcination conditions are crucial for obtaining porous solids. If calcination is carried out in air at 400 °C, although pillared powders and films are again obtained, surface areas are only ca. 40 m2 g–1(B.E.T., N2, 77 K).Furthermore, higher calcination temperatures (500 °C, under N2) give rise to X-ray amorphous materials, again having high surface areas and narrow pore-size distributions. All the materials can be processed in thin-film form without loss of textural characteristics.