An extensive screening of representative molecules of a post-hydrothermal process side stream has been performed with the aim of producing a gas mixture rich in hydrogen by catalytic aqueous phase reforming. The survey enlightens possible routes of valorisation of these by-products, scarcely investigated with other processes so far. The influence of reaction temperature was studied in the 230-270 degrees C range, looking at both the composition of the gas phase and the characterization of the liquid products. Indeed, the information coming from the condensed phase may provide relevant insights on the components that are not easily reformed, and that should be studied to improve the performance of the process. Binary and ternary mixtures of four selected compounds were tested to investigate synergistic and inhibiting effects, going towards the direction of a real biorefinery stream. The spent alumina-supported catalyst was characterized, outlining possible deactivation mechanisms of the catalytic system, and reused in two successive tests.

In this Article, we present an easy, quick, and scalable route, based on anodic oxidation, for the preparation of mesoporous SnO2 as an efficient electrocatalyst for the CO2 reduction reaction (CO2RR). Crystallographically interconnected SnO2 nanocrystals with abundant grain boundaries, high specific surface area, and easily accessible porosity result to be active and selective for the CO2RR. This electrocatalyst shows faradaic efficiency (FE) of about 95% at -0.97 and -1.06 V versus reversible hydrogen electrode (RHE) toward the formation of predominant HCOOH and minor CO. A peak FE value of 82% for the HCOOH production is obtained at -1.06 V vs RHE. High HCOOH partial current densities of 10.2 and 15.3 mA cm(-2) are observed at -0.97 and -1.15 V vs RHE, respectively. Thorough electrochemical characterizations demonstrate that the synthesized SnO2-based gas diffusion electrode allows efficient diffusion of CO2 even at high kinetics because of the highly open porous structure. The good understanding of the catalyst behavior is achieved also after the electrode testing, and it shows that the proposed preparation route results in a stable and durable material. The here reported promising results can be exploited for developing high-performance and sustainable electrocatalysts with a high potentiality to be implemented in real CO2 conversion devices.

Wet air oxidation (WAO) of lignocellulosic biomasses is a promising route for the production of renewable and valuable compounds, involving air as primary oxidant and mild reaction temperatures. In this work, an industrial residue of bioethanol production, steam exploded lignin derived from wheat straw, undergoes a WAO process with the aim to achieve more insights on the process performances in terms of potential yields of aromatic compounds and carboxylic acids (CAs). The experiments were carried out in a pressurized 50 ml batch reactor loaded with water or other aqueous solutions as solvent, the standard conditions were 150 °C of temperature, 20 bar of initial air pressure and 2 h. Afterwards, several solvothermal pretreatments were applied in order to depolymerize and solubilize lignin under inert atmosphere; the residues-free solutions obtained in this way were used as substrate for the WAO reaction. The choice of the pretreatment temperature, solvent alkalinity and presence of perovskite catalysts were evaluated with regard to the mass yields of resulting aromatic compounds and CAs, their carbon content, and the products distribution. Best performance exhibits a lignin dissolution ratio of 53% with 1.3% of yield towards aromatic compounds, where vanillin is the principal product (59.1%), but also the 32% of yield in CAs with glycolic acid as major product (40.9%).

Low-cost manganese oxide, MnOx-based electrocatalysts, containing α-MnO2 and mixed α-Mn2O3/α-MnO2 phases, were synthesized by scalable anodic and cathodic electrodeposition methods, respectively. Their morphological and chemical composition were characterized by means of Field Emission Scanning Electronic Microscopy (FESEM), X-Ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). These electrodes were tested for the electro-oxidation of a recalcitrant molecule (i.e. phenol) in a lab-scale high temperature and high pressure (HTHP) batch electrocatalytic reactor. Their electrocatalytic activity was compared with that of state-of-the-art anodes for phenol electro-oxidation: antimony-doped tin oxide (SnO2–Sb5+) and ruthenium oxide (RuO2): first, under standard ambient conditions, and then, under the conditions of a Polymeric Electrolyte Membrane (PEM) electrolyzer (i.e. 85 °C and 30 bar) and of mild Catalytic Wet Air Oxidation (CWAO, i.e. 150 °C and 30 bar). Both reaction time and current density were varied to investigate their effect in the performances of the system as well as on the reaction mechanism. Both MnOx electrodes reported enhanced conversion efficiencies, up to ∼75%, at the highest pressure and temperature, and at the lowest applied current density, which influenced the process by improving dissolution of the O2 evolved, the reaction kinetics and thermodynamics, and by minimizing irreversibilities, respectively. The here reported MnOx films achieved conversion and mineralization efficiencies comparable to Sb-SnO2 (that is the more toxic) and RuO2 (that is more expensive) materials, operating under mild CWAO operation conditions, which demonstrate the potential of the electrocatalytic HTHP process as a sustainable advanced oxidation technology for wastewater treatment or electrosynthesis applications.

The hydrodeoxygenation (HDO) of guaiacol has been chosen as a model process for the upgrading of lignin-derived bio-oils. Tests were carried out in a batch reactor at 350 °C, 4000 kPa of H2, in the presence of several Mo-based catalysts prepared by impregnation of ammonium molybdate on SiO2, Al2O3, NaY zeolite, MgO, activated carbon, and graphite. These materials have been characterized by means of: N2 physisorption, XRD, FESEM/EDS, XPS, TPR-H2, and TPD-NH3, with the aim of correlating the physical and chemical properties of the prepared samples with the resulting features in the HDO reaction. Mo on activated carbon showed the best performances towards guaiacol demethoxylation, exhibiting complete conversion, 72 % of selectivity to phenol, and 19 % to p- and o-cresol. The high surface area and low acidity of activated carbon allow good dispersion of MoOx which exhibits characteristic fragments with a lamellar shape, able to provide a large active surface with localized acidity.

The development of an efficient model of integrated biorefinery based on renewable lignocellulosic biomasses seems to be fundamental to ensure a sustainable production of fuels and chemicals. Generally, cellulose and hemicellulose are hydrolyzed into the corresponding sugars constituting their structures and then transformed mainly into ethanol, while the lignin fraction is considered as a waste and it is mostly burned to produce energy or steam. Despite years of efforts, the development of a commercial plant for biomass-to-biofuel conversion is still economically tricky. Coupling the production of fuels with high-added value chemicals may be fundamental to achieve the economic sustainability of these processes. The aim of our work has been to take a residue, steam exploded lignin derived from wheat straw, and to transform it firstly into substituted phenols and secondly into carboxylic acids through an oxidative process with air as first oxidant agent. Perovskite-type oxides have shown high oxidative activity in similar processes [1], therefore several perovskites have been prepared through the solution combustion synthesis (SCS) and tested in the oxidation of lignin. The experiments have been carried out in a pressurized batch reactor loaded with water or aqueous solutions as solvent. The process takes 1-4 hours with temperatures ranging from 150 to 250°C and air pressure between 20 and 50 bar, showing lignin dissolution up to 80%. A µGC analyzer has been adopted to monitor the undesired production of CO2, while the reaction mixture is analyzed by means of GC-MS and ionic chromatography. Catalysts such as LaMnO3, CeFeO3 and LaFeO3 have been characterized through XRD, XPS, TPR and FE-SEM analysis. Best catalytic performances have been achieved with a basic environment and a solubilization pre-treatment of the raw lignin before the CWAO reaction, giving a 8% mass yield in aromatics and showing phenol, vanillin and p-hydroxybenzaldehyde as main compounds. Moreover, the obtained yield in organic acids is up to 12%, main products are lactic acid, glycolic acid and succinic acid. Even though the yields are limited, the novelty of the process is the generation of saturated C4, C5 and C6 dicarboxylic acids not observed before in similar processes [2]. [1] Bernardi M., Deorsola F. A., Fino D., Russo N., Waste and Biomass Valorization, 2014, 5 (5), 857-863. [2] Ma R., Guo M., Zhang X., ChemSusChem, 2014, 7 (2), 412-415.