Design approach for the sustainable synthesis of sulfonated biomass-derived hydrochars and pyrochars for the production of 5-(hydroxymethyl)furfural

The sustainable synthesis of carbon-based sulfonated acid catalysts from biomass is of paramount importance from the perspective of sustainability. However, the traditional pyrolysis method leads to low solid yields and poor carbon stability. A cascade synthesis is here proposed, combining hydrothermal carbonization and pyrolysis, to produce a “high-quality” carbon-based precursor, followed by its sulfonation to increase the pristine acidity. The proposed multi-step preparation is effective when each step is optimized, primarily the hydrothermal carbonization, which should be carefully optimized. A chemometric approach was employed to optimize the hydrochar synthesis, using microcrystalline cellulose as starting feedstock. The identified optimal reaction conditions were applied to the hydrothermal carbonization of hazelnut shells, which is a more complex but cheaper feedstock, and the obtained hydrochars were pyrolyzed to produce pyrochars. The most promising chars were sulfonated and tested as heterogeneous acid catalysts in the aqueous conversion of fructose to 5-(hydroxymethyl)furfural, a promising platform chemical of great industrial interest, obtaining maximum yields of about 40 mol%. These promising results pave the way for the use of such wastes as efficient acid catalysts for the synthesis of 5-(hydroxymethyl)furfural, contributing to ensure the biomass circular exploitation

Oscillatory behaviour of ni supported on zro2 in the catalytic partial oxidation of methane as determined by activation procedure

Ni/ZrO2 catalysts, active and selective for the catalytic partial oxidation of methane to syngas (CH4-CPO), were prepared by the dry impregnation of zirconium oxyhydroxide (Zhy) or monoclinic ZrO2 (Zm), calcination at 1173 K and activation by different procedures: oxidation-reduction (ox-red) or direct reduction (red). The characterization included XRD, FESEM, in situ FTIR and Raman spectroscopies, TPR, and specific surface area measurements. Catalytic activity experiments were carried out in a flow apparatus with a mixture of CH4:O2 = 2:1 in a short contact time. Compared to Zm, Zhy favoured the formation of smaller NiO particles, implying a higher number of Ni sites strongly interacting with the support. In all the activated Ni/ZrO2 catalysts, the Ni–ZrO2 interaction was strong enough to limit Ni aggregation during the catalytic runs. The catalytic activity depended on the activation procedures; the ox-red treatment yielded very active and stable catalysts, whereas the red treatment yielded catalysts with oscillating activity, ascribed to the formation of Niδ+ carbide-like species. The results suggested that Ni dispersion was not the main factor affecting the activity, and that active sites for CH4-CPO could be Ni species at the boundary of the metal particles in a specific configuration and nuclearity

Solid base catalysed 5-HMF oxidation to 2,5-FDCA over Au/hydrotalcites: fact or fiction?

Nanoparticulate gold has emerged as a promising catalyst for diverse mild and efficient selective aerobic oxidations. However, the mechanism of such atom-economical transformations, and synergy with functional supports, remains poorly understood. Alkali-free Mg-Al hydrotalcites are excellent solid base catalysts for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furan dicarboxylic acid (FDCA), but only in concert with high concentrations of metallic gold nanoparticles. In the absence of soluble base, competitive adsorption between strongly-bound HMF and reactively-formed oxidation intermediates site-blocks gold. Aqueous NaOH dramatically promotes solution phase HMF activation, liberating free gold sites able to activate the alcohol function within the metastable 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) reactive intermediate. Synergistic effects between moderate strength base sites within alkali-free hydrotalcites and high gold surface concentrations can afford highly selective and entirely heterogeneous catalysts for aqueous phase aldehyde and alcohol cascade oxidations pertinent to biomass transformation