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Fructose is one of the most important aldoses and has been gaining attention as the starting material for the synthesis of biobased platform and high-added value chemicals such as 5-hydroxymethylfurfural (5-HMF), levulinic acid and lactic acid. However, due to its low natural occurrence, fructose is produced from glucose, an abundant hexose, via isomerization. Currently, the conventional industrial process utilizes glucose isomerase as a catalyst and is therefore subjected to the limitations of enzymatic reactions. Consequently, an alternative efficient solid catalyst is required that will exhibit high activity, selectivity and stability/reusability. Toward this end, we have demonstrated the effectiveness of using natural MgO, derived from simple calcination of magnesite ores, as a low cost catalyst with increased basicity. A series of industrial and laboratory prepared natural MgO materials with different morphology, porosity and basicity were investigated and the optimum catalyst afforded 44.1 wt % glucose conversion and 75.8 wt % fructose selectivity (33.4 wt % fructose yield), at 90 °C for a 45 min reaction in aqueous solution. The activity of the MgO catalysts was directly correlated with their basicity, which in turn depended on their crystal size, surface area and composition. CaO impurities of the natural MgO materials generated strong basic sites that enhanced glucose conversion but at the expense of fructose selectivity. The stability and reuse of the optimum catalyst was confirmed for at least 4 cycles of reaction–regeneration, whereas the mechanism of glucose isomerization was validated via a first-order kinetic modeling set.

The valorization of lignin that derives as by product in various biomass conversion processes has become a major research and technological objective. The potential of the production of valuable mono-aromatics (BTX and others) and (alkyl)phenols by catalytic fast pyrolysis of lignin is investigated in this work by the use of ZSM-5 zeolites with different acidic and porosity characteristics. More specifically, conventional microporous ZSM-5 (Si/Al = 11.5, 25, 40), nano-sized (≤20 nm, by direct synthesis) and mesoporous (9 nm, by mild alkaline treatment) ZSM-5 zeolites were tested in the fast pyrolysis of a softwood kraft lignin at 400–600°C on a Py/GC-MS system and a fixed-bed reactor unit. The composition of lignin (FT-IR, 2D HSQC NMR) was correlated with the composition of the thermal (non-catalytic) pyrolysis oil, while the effect of pyrolysis temperature and catalyst-to-lignin (C/L) ratio, as well as of the Si/Al ratio, acidity, micro/mesoporosity and nano-size of ZSM-5, on bio-oil composition was thoroughly investigated. It was shown that the conventional microporous ZSM-5 zeolites are more selective toward mono-aromatics while the nano-sized and mesoporous ZSM-5 exhibited also high selectivity for (alkyl)phenols. However, the nano-sized ZSM-5 zeolite exhibited the lowest yield of organic bio-oil and highest production of water, coke and non-condensable gases compared to the conventional microporous and mesoporous ZSM-5 zeolites.

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Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst.

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