Catalysts are indispensable for effective utilization of limited resources and efficient progress of chemical reactions. Heterogeneous solid catalysts are easily separable and reusable after reactions, and moreover they are durable and applicable under a wide range of reaction conditions. Prof. Atsushi Fukuoka have developed solid catalysts with high activity for the depolymerization of cellulose and chitin, and succeeded in highly selective synthesis of glucose, N-acetylglucosamine and oligosaccharides. He has also achieved low-temperature oxidation of ethylene using silica-supported Pt catalysts, clarified the reaction mechanism and applied the catalysts to freshness preservation of fruits and vegetables, enabling the reduction of food waste. His major achievements are listed below.

1. Depolymerization of cellulose by solid catalysts
Utilization of renewable biomass as a feedstock contributes to establishing low-carbon processes in chemicals synthesis. The main component of plant biomass is cellulose, which may be used as a raw material for chemicals after depolymerization. However, cellulose has a robust crystal structure and is difficult to degrade. In addition, glucose produced by depolymerization is prone to side reactions to form undesirable byproducts under typical reaction conditions. Prof. Fukuoka came up with an idea to use solid catalysts for cellulose depolymerization and found that when the reaction was carried out under pressurized hydrogen using supported metal catalysts, hydrolytic hydrogenation of cellulose proceeded to form sorbitol via glucose. This was the first solid-catalyzed cellulose depolymerization, and it triggered similar research works. Then, he focused on cellulose hydrolysis and presented a new methodology using carbon catalysts bearing weak acid sites such as carboxy groups and a mix-milling treatment of the catalyst and cellulose. The mix-milling treatment increased the contact between the solid catalyst and the solid substrate, allowing cellulose to be adsorbed on the carbon surface and hydrolyzed at β-1,4-glycosidic bonds by the weak acids. This method enabled the rapid synthesis of glucose, and water-soluble cello-oligosaccharides (trimer to hexamer) were successfully produced in good yields in a flow system. These reactions were realized by taking advantage of the high durability of the solid catalysts and by broadening the range of applicable conditions. The water-soluble cello-oligosaccharides are highly valuable to work as biostimulants for plants.

2. Depolymerization of chitin by solid catalysts
Prof. Fukuoka has also studied the depolymerization of chitin, a marine biomass containing nitrogen. Chitin is a polymer of N-acetylglucosamine (NAG) linked by β-1,4-glycosidic bonds and has a similar structure to cellulose. Chitin is contained in the shells of crab and prawn and is the second largest biomass resource next to cellulose. Besides glycosidic bonds, chitin has amide groups which might be hydrolyzed during depolymerization, but deacetylated chitosan is less valuable than NAG. He showed that chitin can be efficiently depolymerized by mechanocatalysis in applying the cellulose depolymerization method. When chitin powder is mix-milled with sulfuric acid, the acidic sites cleave the glycosidic bond but retains the amide group, resulting in the formation of chitin oligosaccharides with high selectivity. The reaction mechanism was investigated in detail, and it was found that the macroscopic force of the ball milling selectively activates the glycosidic bond and promotes both protonation and cleavage at the glycosidic bonds. Further hydrolysis of the oligosaccharides gave NAG. Recently, he found that an activated carbon catalyst having weak acid sites hydrolyzes chitin to chitin-oligosaccharides selectively in the presence of mechanical milling. This catalyst easily adsorbs large polysaccharides and can hydrolyze large polymers to small oligomers more selectively and quickly than other catalysts. Chitin oligosaccharides are useful as biostimulants like cello-oligosaccharides. In addition, he investigated the conversion of NAG, in which reduction of NAG gave a sugar alcohol (ADS) and dehydration of ADS produced a new bicyclic amide alcohol (ADI). In this way, starting from depolymerization of chitin to NAG, he demonstrated the synthesis of various organonitrogen compounds. Using chitin as a source, nitrogen as well as carbon is renewable.

3. Low-temperature oxidation of ethylene by silica-supported platinum catalysts and their application to freshness preservation of fruits and vegetables
Prof. Fukuoka has been studying oxidation reactions catalyzed by platinum nanoparticles supported on porous silica, and found that ethylene is oxidized to carbon dioxide and water even at temperatures as low as 0 °C. This low-temperature oxidation occurs when Pt and silica are combined. The structure-activity correlations were studied, in which the combination of hydrophobic silica and Pt is important in activation of adsorbed ethylene and oxidation to CO₂. Specifically, Pt surface is the active site, and that hydrophobic siloxanes on silica effectively remove water to maintain steady-state activity. Furthermore, he applied this catalyst to the freshness preservation. Even a trace amount of ethylene accelerates the aging and ripening of fruits and vegetables, and thus continuous removal of ethylene is a key to minimizing the food waste. He showed that silica-supported Pt catalysts can oxidize trace amounts of ethylene released from fruits and vegetables after harvesting, thus inhibiting their ripening. This catalyst, named "Platinum Catalyst," has been practically used in vegetable compartments of refrigerators and in storage houses, contributing to the improvement of vegetable yields and the reduction of food waste. The catalyst in the storage house has shown the effect of freshness preservation for more than three years. This is attributed to the high durability of the Platinum Catalyst.

As described above, Prof. Fukuoka has revealed that the glycosidic bond of cellulose can be efficiently depolymerized by mix-milling of cellulose and carbon catalysts and realized high-speed synthesis of glucose and selective formation of cello-oligosaccharides. He also developed a mechano-catalytic depolymerization of chitin to produce chitin-oligosaccharides and NAG, and application of NAG for the synthesis of organonitrogen compounds. Furthermore, low-temperature oxidation of ethylene using silica-supported platinum catalysts was attained and applied to the freshness preservation of fruits and vegetables. These results have greatly contributed to the progress of chemistry of heterogeneous solid catalysts. Therefore, his achievements are recognized as worthy of the Chemical Society of Japan Award.