Research topics

1. Catalytic process development for valorization of woody biomass

Cellulose, the primary component of woody biomass, is the most abundant source of carbohydrate resource on the planet. It is an excellence resource of chemical production because of its inedible nature. We have developed a process for hydrolysis of cellulose to glucose using heterogeneous carbon catalysts in a batch and slurry flow system to achieve high glucose yield of 86 % (Fig. 1).

Progress in fiscal year 2018: We have focused our attention towards synthesis of cello-oligosaccharides from cellulose by utilizing the weakly acidic sites of carbon catalyst and a semi-flow reactor. Cello-oligosaccharides act as elicitors to improve the immune response of plants and they have the potential to reduce the use of pesticides and facilitate sustainable agriculture of crops. We have also developed a method for the quantification of individual cello-oligosaccharides by using MALDI-TOF/MS.

Fig. 1: Hydrolysis of cellulose to cello-oligosaccharides and glucose over weakly acidic carbon catalysts.
References
  1. P. Chen, A. Shrotri, A. Fukuoka
    Soluble Cello-Oligosaccharides Produced by Carbon-Catalyzed Hydrolysis of Cellulose, ChemSusChem. 12, 2576-2580 (2019).
  2. A. Shrotri, H. Kobayashi, A. Fukuoka,
    Cellulose Depolymerization over Heterogeneous Catalysts, Acc. Chem. Res. 51, 761-768 (2018).
  3. A. Shrotri, H. Kobayashi, H. Kaiki, M. Yabushita, A. Fukuoka
    Cellulose hydrolysis using oxidized carbon catalyst in a plug-flow slurry process, Ind. Eng. Chem. Res. 56, 14471-14478 (2017).
  4. H. Kobayashi, H. Kaiki, A. Shrotri, K. Techikawara, A. Fukuoka
    Hydrolysis of woody biomass by a biomass-derived reusable heterogeneous catalyst, Chem. Sci. 7, 692-696 (2016).
  5. H. Kobayashi, M. Yabushita, T. Komanoya, K. Hara, I. Fujita, A. Fukuoka
    High-Yielding One-Pot Synthesis of Glucose from Cellulose Using Simple Activated Carbons and Trace Hydrochloric Acid, ACS Catal. 3, 581-587 (2013).

2. Hydrolysis of marine biomass and synthesis of nitrogen-containing compounds

Chitin, present in the exoskeleton of crustaceans such as crabs and shrimps, is a naturally abundant polymer of N-acetylglucosamine (NAG). It has the potential to be a sustainable feedstock for synthesis of value-added nitrogen containing compounds. However, the conventional methods for selective synthesis of NAG from chitin requires a large amount of hydrochloric acid or a long reaction time in the presence of enzymes. We succeeded to produce water-soluble oligosaccharides containing several NAG units by impregnating chitin with a small amount of sulfuric acid and then treating it in a planetary ball mill. Subsequent hydrolysis of these oligosaccharides produced NAG in good yield. Current research focus is towards development of catalytic processes for synthesis of value-added chemical from NAG.

Progress in fiscal year 2018: NAG was further converted to an acetylated form of monoethanolamine by retro-aldol reaction and subsequent hydrogenation in the presence of a base and Ru/C catalyst (Fig. 2). The retro-aldol reaction cleaved the bond between C2 and C3 carbon atoms of NAG. In contrast, the retro-aldol reaction of glucose, also a hexose, cleaves the bond between the C3 and C4 carbon atoms. DFT calculation of the reaction steps showed that the formation of an imine group required for the cleavage of C3-C4 bond was energetically disfavored. The formation of imine would lead of loss of stabilization achieved by resonance of the amide group. Following the retro-aldol reaction we oxidized the acetylated-monoethanolamine in the presence of Ru/C catalyst and oxygen to the N-acetyl form of glycine, a standard amino acid.

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Fig. 2: Conversion of N-acetylglucosamine (NAG) to an amino acid.
References
  1. T. Sagawa, H. Kobayashi, C. Murata, Y. Shichibu, K. Konishi, A. Fukuoka
    Catalytic Conversion of a Chitin-Derived Sugar Alcohol to an Amide-Containing Isosorbide Analog, ACS Sustain. Chem. Eng. 7, 14883-14888 (2019).
  2. K. Techikawara, H. Kobayashi, A. Fukuoka
    Acetylglucosamine to Protected Amino Acid over Ru/C Catalyst, ACS Sustain. Chem. Eng. 6, 12411-12418 (2018).
  3. H. Kobayashi, K. Techikawara, A. Fukuoka
    Hydrolytic hydrogenation of chitin to amino sugar alcohol, Green Chem. 19, 3350-3356 (2017).
  4. M. Yabushita, H. Kobayashi, K. Kuroki, S. Ito, A. Fukuoka
    Catalytic Depolymerization of Chitin with Retention of N-Acetyl Group, ChemSusChem. 8, 3760-3763 (2015).

3. Low temperature oxidative removal of ethylene with Pt nanoparticles supported on mesoporous silica

Ethylene is a potent plant hormone released by fruits and vegetables that intensifies the ripening and decay of stored fruits and vegetable even when it is present in very small amounts. Removal of ethylene at room temperature and even at 0 ?C is essential to preserve agricultural commodities during storage and transportation. We have found that platinum nanoparticles supported on mesoporous silica have an excellent ability to remove ethylene at low temperatures (Fig. 3). This catalyst can completely remove trace amounts of ethylene (less than 50 ppm) even at 0 C. Commercial variant of this catalyst are installed in the refrigerators sold by Hitachi Appliances since 2015. Furthermore, we found that the use of ruthenium-platinum bimetallic catalyst was effective in removing nitrogen and sulfur containing compounds responsible for foul smell inside a refrigerator. Based on these findings, Hitachi Appliances launched a new line of refrigerators in Aug 2017 that houses platinum-ruthenium catalyst in vegetable and vacuum chilled sections for meat and vegetable storage.

Progress in fiscal Year 2018: Mechanistic investigation revealed that the activity of supported platinum catalyst increased when the number of silanol groups on the support was lower making the surface hydrophobic. It was presumed that the hydrophobic surface prevented the accumulation of water produced in the oxidation reactions which would otherwise limit the access to Pt nanoparticles. Furthermore, the rate of CO2 generation from ethylene oxidation was lower than expected in the initial stages of the reaction, which suggested the accumulation of intermediates on the catalyst. Infrared spectroscopy under operando conditions and extraction of products from catalyst surface revealed the presence of formate and acetate species as possible intermediates.

Fig. 3: Oxidation of ethylene over a mesoporous silica-supported platinum catalyst.
Reference
  1. S.S. Satter, J. Hirayama, K. Nakajima, A. Fukuoka
    Low temperature oxidation of trace ethylene over Pt nanoparticles supported on hydrophobic mesoporous silica, Chem. Lett. 47, 1000-1002 (2018).
  2. S.S. Satter, T. Yokoya, J. Hirayama, K. Nakajima, A. Fukuoka
    Oxidation of Trace Ethylene at 0 c over Platinum Nanoparticles Supported on Silica, ACS Sustain. Chem. Eng. 6, 11480-11486 (2018).
  3. C. Jiang, K. Hara, A. Fukuoka
    Low-Temperature Oxidation of Ethylene over Platinum Nanoparticles Supported on Mesoporous Silica, Angew. Chem. Int. Ed., 52 (24), 6265-6268 (2013).

4. Catalyst development for methane conversion.

Efficient conversion of methane to synthesis gas (CO + H2) is a key step in utilization of natural gas. However, the current industrial steam reforming process (CH4 + H2O CO + 3H2) requires temperatures exceeding 800 C. The partial oxidation of methane (CH4 + 1/2 O2 CO + 2H2), which is still under development, also requires temperatures above 750 C. We produced rhodium sub-nanocluster catalysts with a diameter of 0.6 nm on MOR zeolite by ion exchange and calcination. The catalyst was active at a temperature of 600 C, even at a very high space velocity of 1.2 ~ 106 mL h-1 g-1, resulting in 84% conversion of methane with 91% CO selectivity and H2/CO ratio of 2. The catalyst did not lose activity after 50 h of continuous reaction and the turnover number for CO formation reached 2.6 ~ 106. The low reaction temperature would reduce the process costs by allowing the use of common stainless-steel reactors that are not useful above 650 C. Progress in fiscal Year 2018: Cobalt is a cheaper alternative catalyst for methane oxidation, but it readily oxidizes under the reaction condition and is therefore not useful as single metal catalyst. However, when a Co/MOR catalyst is prepared with 0.005-0.05 wt% rhodium content high activity for methane oxidation is achieved with CO selectivity of 91% at 650 C (space velocity 1,200,000 mL h-1 g-1, H2/CO ratio 2.0, methane conversion 86%). The enhancement of the activity was attributed to atomic distribution of rhodium on cobalt particles having a diameter of 1.5 nm (Fig. 4). The rhodium atom facilitated the generation of surface hydrogen species that maintained the zero valent state of nearby cobalt particles via the spillover mechanism.

Fig. 4: Structure of Rh-Co/MOR catalyst for methane partial oxidation and scheme showing hydrogen spillover.[1,2]
Reference
  1. Y. Hou, S. Nagamatsu, K. Asakura, A. Fukuoka, H. Kobayashi
    Trace mono-atomically dispersed rhodium on zeolite-supported cobalt catalyst for the efficient methane oxidation, Commun. Chem. 1 (2018).
  2. Y. Hou, S. Ogasawara, A. Fukuoka, H. Kobayashi
    Zeolite-supported rhodium sub-nano cluster catalyst for low-temperature selective oxidation of methane to syngas, Catal. Sci. Technol. 7, 6132-6139 (2017).