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Metal stannates catalyse glucose–fructose isomerisation in methanol by base-catalysis via a proton-transfer mechanism, while the reaction is catalysed heterogeneously in isopropanol and higher alcohols by Sn–OH sites.

Lignin, the world’s most abundant biopolymer with high aromaticity, has huge potential as a renewable feedstock replacing petroleum for the production of chemicals, fuels and functional materials. The enhanced utilization of lignin would improve the economic viability of existing pulp and paper mills, as well as lignocellulosic biorefineries, where lignin is highly available, but mostly incinerated for energy recovery. Catalysis could be of crucial importance to improve current depolymerization strategies, and hence contribute to the more sustainable and responsible use of terrestrial resources. In the present study, the impact of different homogeneous transition-metal catalysts on the oxidative depolymerization of a technical softwood kraft lignin was investigated. The reactions were carried out using molecular oxygen under rather mild operating conditions and the produced aromatic monomers included, among others, vanillin, vanillic acid and acetovanillone. The best performing system incorporated a VO(acac)2-Cu(OAc)2 (V-Cu) catalyst, resulting in a bio-oil yield of approximately 50% and a total increase in aromatic monomers of 27%, on a weight basis. Moreover, a favorable combined effect between VO(acac)2 and Cu(OAc)2 was suggested by NMR spectroscopy. UHPLC–HRMS and corresponding statistical analysis revealed a more than 30-fold increase in two aromatic molecules with an oxoacetic functionality and oxalic acid as well as a focusing effect on selected molecules, when employing the V-Cu catalyst. The findings of this study indicate that the V-Cu catalyst system is promising for the efficient conversion of technical lignin into value-added aromatic chemicals. However, catalyst recycling and reuse must be demonstrated, for successful implementation under industrial conditions.

In this study, the performance of an In2O3/ZrO2 catalyst for hydrogenation of CO2 to methanol is reported in the presence of typical impurities of industrial CO2 feed gas streams. Experiments were performed with defined amounts of SO2, H2S, NO2, NH3 and hydrocarbons purposely added to the reaction mixture under industrially relevant conditions (225–275 °C, 50 bar total pressure, H2 : CO2 = 3 : 1). Comparative studies – with and without added impurities – further relate the observed effects to the behaviour of the commercial Cu/ZnO/Al2O3 methanol catalyst under identical treatments. Elemental analysis was used to determine the amount of sulphur, nitrogen and carbon residing on the catalyst after poisoning and after methanol synthesis. Moreover, temperature programmed desorption (TPD), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) allowed identifying potential catalyst poisons formed on the catalyst surface. This work discloses that H2S and SO2 impurities led to drastic deactivation of the In2O3/ZrO2 catalyst (due to indium sulfide and -sulphate formation), while NH3, NO2 and hydrocarbon impurities have no major effect on the methanol production.

Ceria-supported ruthenium hydroxide catalysts, Ru(OH)x/CeO2, comprising micro- A nd nanoparticle supports were prepared, characterized and examined for the catalytic aerobic oxidation of glycolaldehyde (GAD) to formic acid (FA) in water under mild and base-free conditions. Under optimized reaction conditions, both of the examined catalyst types gave a high FA yield of around 80% at full GAD conversion with low CO2 formation (>95% carbon balance), while intermediate oxidation products were obtained under milder conditions and humins dominated under harsher conditions. The nanoparticle catalysts were more active than analogous catalysts based on microparticle ceria, which had a lower BET surface area and lower content of surface Ru(OH)x species relative to other Ru species. Notably, the superior nanoparticle-based catalyst also proved to be reusable in three consecutive reaction runs with essentially unchanged catalytic performance. This study demonstrates a benign and green protocol to convert GAD-a versatile platform molecule obtainable from biomass-derived carbohydrates-into the large-volume commodity chemical FA which has multiple industrial applications.

Simple sugars show promise as substrates for the formation of fuels and chemicals using heterogeneous catalysts in alcoholic solvents. Sn-Beta is a particularly well-suited catalyst for the cleavage, isomerization and dehydration of sugars into more valuable chemicals. In order to understand these processes and save resources and time by optimising them, kinetic and mechanistic analyses are helpful. Herein, we study substrate entry into the Sn-Beta-catalysed methyl lactate process using abundant hexose substrates. NMR spectroscopy is applied to show that the formation of methyl lactate occurs in two kinetic regimes for fructose, glucose and sucrose. The majority of methyl lactate is not formed from the substrate directly, but from methyl fructosides in a slow regime. At 160 °C, more than 40% of substrate carbon are masked (i.e. reversibly protected in situ) as methyl fructosides within a few minutes when using hydrothermally synthesised Sn-Beta, while more than 60% methyl fructosides can be produced within a few minutes using post-synthetically treated Sn-Beta. A significant fraction of the substrate is thus masked by rapid methyl fructoside formation prior to subsequent slow release of fructose. This release is the rate-limiting step in the Sn-Beta-catalysed methyl lactate process, but it can be accelerated by the addition of small amounts of water at the expense of the maximum methyl lactate yield.

Magnetic nickel ferrite (NiFe2O4) nanoparticles were exploited as stable and easily separable heterogeneous catalysts for catalytic transfer hydrogenation (CTH) of furfural to furfuryl alcohol with 2-propanol as both the hydrogen source and the solvent providing 94% product yield at 180 °C after 6 h of reaction. The magnetic properties of the catalysts provided facile recovery using an external magnet after reaction allowing it to be reused in five reaction cycles without loss of catalytic performance. Importantly, the NiFe2O4 nanoparticles were also applicable to CTH of other alkenyl/allyl/aromatic aldehydes affording over 94% selectivity towards the targeted alcohol products, thus being attractive as highly universal catalysts for CTH of aldehydes.

Sucrose is by far the industrially most abundant simple carbohydrate with a production volume of more than 160 million metric tons from sugar cane and sugar beet per year. Many promising pathways towards bio-based organic compounds use, however, fructose as the pathway substrate. Hence, a chemocatalytic approach to convert sucrose into fructose would provide a means to channel sucrose into pathways for sugar valorization. Here, we show that a variety of heterogeneous zeolite catalysts with balanced Bronsted and Lewis acidity enable a simple route for the conversion of sucrose to more than 80% fructosides or fructose at 100 °C. The catalysts can encompass aluminium or tin Lewis acidic sites in various zeolite frameworks. The reaction proceeds in volatile alcohol solvents and broadly enables the channelling of sucrose into processes that use fructose as the pathway substrate.

The oxidative dehydrogenation of various aliphatic amines to their corresponding nitrile compounds using RuO2/Al2O3 catalysts in air was successfully applied to a continuous flow reaction. Conversions of amines (up to >99%) and yields of nitriles (up to 77%) varied depending on reaction conditions and the amine utilised. The presence of water was found to be important for the activity and stability of the RuO2/Al2O3 catalyst. The Hammett relationship and in situ infrared spectroscopy were applied to divulge details about the catalytic mechanism of the oxidative dehydrogenation of amines over RuO2/Al2O3 catalysts.

The isomerization of erythrose (ERO) was studied in water over commercially available large-pore zeolites, e.g. H-Y, H-USY and H-beta. Among the employed zeolites, H-USY(6) was found to efficiently isomerize the sugar, yielding 45% erythrulose (ERU), 42% ERO and 3% of the epimer threose (THO) (corresponding to the equilibrium mixture), i.e. total tetrose yield 90%, after reaction for 5–7 h at 120 °C. Changing the solvent from water to methanol decreased the yield of ERU markedly to 18% and gave only a total yield of tetroses of 27% which is significantly lower than that obtained in water. Hence, the results demonstrate that water is the preferred solvent compared to lower alcohols for zeolite-catalyzed tetrose isomerization, which is opposite to what has been found previously for analogous pentose and hexose isomerization. A reuse study revealed further that H-USY(6) could be applied for at least five reaction runs with essentially unchanged activity and without significant aluminum leaching from the catalyst. The use of benign reaction conditions and an industrially pertinent solid catalyst in combination with water establishes a new, green tetrose isomerization protocol.

V2O5/TiO2 and heteropoly acid promoted V2O5/TiO2 catalysts were prepared and characterized by N2 physisorption, XRPD and NH3-TPD. The influence of the calcination temperature from 400 to 700 °C on crystallinity and acidic properties was studied and compared with the activity for the selective catalytic reduction (SCR) of NO with ammonia. The SCR activity of heteropoly acid promoted catalysts was found to be much higher than for unpromoted catalysts. The stability of heteropoly acid promoted catalysts is dependent on calcination temperature and there is a gradual decrease in SCR activity and acidity with increase in calcination temperatures. Furthermore, the heteropoly acid promoted V2O5/TiO2 catalysts showed excellent alkali deactivation resistance and might therefore be alternative deNOx catalysts in biomass fired power plants.