With diminishing fossil resources and rising concerns about global warming caused by greenhouse gas emissions, biomass is regarded as a promising alternative to non-renewable fossil resources for the sustainable supply of fuels and chemicals. Because of its abundant content of carbon, biomass is considered as the best source to replace fossil fuels for producing various biofuels such as biodiesel, ethanol, and dimethylfuran. It can be transformed into numerous value-added oxygen-containing heterocyclic compounds through a series of chemical reactions including hydrolysis, dehydration, oxidation, hydrogenation, and hydrogenolysis.
Now (2020), scientists at Brookhaven National Laboratory have investigated how a plant derivative can be converted into fuels and other valuable chemicals by placing single atoms of platinum onto titanium dioxide. They have created a catalyst consisting of very low concentrations of platinum on the surface of titanium dioxide and demonstrated how this catalyst significantly improved the rate of breaking a particular carbon-oxygen bond for the conversion of a plant derivative (furfuryl alcohol) into a potential biofuel (2-methylfuran). Their strategy could be used to design stable, active, and selective catalysts based on a wide range of metals supported on metal oxides to produce industrially useful chemicals and fuels from biomass-derived molecules.
In this study, the scientists wanted to find out if adding noble metals to the surfaces of moderately reducible metal oxides might enhance hydrodeoxygenation. The team chose platinum as the noble metal and titanium dioxide (titania) as the metal oxide. After synthesizing the platinum-titania catalyst, they conducted several structural and chemical characterization studies using facilities at Brookhaven and Argonne National Labs. Then, the team performed reactivity studies in which they put the catalyst and furfuryl alcohol in a reactor and detected the products through gas chromatography.
Catalysts for biofuel production from furfuryl alcohol have been at the centre of scientific attention for many years. In 2014, the scientists developed a green and efficient process for the conversion of biomass-derived furfuryl alcohol to ethyl levulinate using eco-friendly solid acid catalysts (zeolites and sulfated oxides) in ethanol. Studies for optimizing the reaction conditions such as the substrate concentration, the reaction time, the temperature, and the catalyst-loading dosage were performed. With SO42-/TiO2 as the catalyst, a high ethyl levulinate yield of 74.6 mol% was achieved using a catalyst load of 5 wt% at 398 K for 2.0 h. The catalyst, which was recovered through calcination, was found to maintain good catalytic activity (47.8 mol%) after three cycles, and it was easily reactivated by re-soaking in an H2SO4 solution.
In 2018, a new technique was proposed to co-produce phenol and activated carbon (AC) from catalytic fast pyrolysis of biomass impregnated with K3PO4 in a hydrogen atmosphere, followed by activation of the pyrolytic solid residues. Lab-scale catalytic fast pyrolysis experiments were performed to quantitatively determine the pyrolytic product distribution, as well as to investigate the effects of several factors on the phenol production, including pyrolysis atmosphere, catalyst type, biomass type, catalytic pyrolysis temperature, and catalyst impregnation content. In addition, the pyrolytic solid residues were activated to prepare ACs with high specific surface areas. The results indicated that phenol could be obtained due to the synergistic effects of K3PO4 and hydrogen atmosphere, with the yield and selectivity reaching 5.3 wt% and 17.8% from catalytic fast pyrolysis of poplar wood with 8 wt% K3PO4 at 550°C in a hydrogen atmosphere. This technique was adaptable to different woody materials for phenol production. Moreover, the gas product generated from the pyrolysis process was feasible to be recycled to provide the hydrogen atmosphere, instead of an extra hydrogen supply. In addition, the pyrolytic solid residue was suitable for AC preparation, using a CO2 activation method, the specific surface area was as high as 1,605 m2/g.
There are several advantages to using the new catalyst: to convert furfuryl alcohol into biofuel, the bond between carbon and oxygen atoms on the side group attached to the ring-shaped part of the molecule must be broken, without producing any reactions in the ring. Typically, the metal catalyst that breaks this bond also activates ring-related reactions; however, the catalyst designed in this study only breaks the side group carbon-oxygen bond.
The complementary experimental and computational framework allows for a detailed understanding of what is happening on the surface of a very complex material in a way that scientists can generalize concepts for the rational design of catalysts. These concepts can help in predicting suitable combinations of metals and metal oxides to perform desired reactions for converting other molecules into valuable products.