(Invited) Integrated Chemocatalytic Conversion of Cellulosic Biomass to Gasoline Blended Fuel Using a Multifunctional Nano-Catalysts
Authors: Niaze Ambereen Aziz , Sunkara Mahendra , Upadhyayula Sreedevi 
Published: August 2024

The Ministry of New and Renewable Energy (MNRE) in India has initiated several programs to promote effective ways of utilizing biomass energy to boost the country's economy. In order to improve the effective use of biomass resources, the initiative for biomass power and cogeneration has adopted the use of bagasse-based cogeneration and biomass power generation in sugar mills. Because of its remarkable characteristics, including its high-octane number, low cetane number, and significant heat of vaporization, bioethanol is considered as a desirable biofuel. In addition, the increased biofuel production, in particular bioethanol, satisfies the criteria of the energy demand. These criteria include the fuel's ability to be blended with gasoline and diesel, as well as standards for low-carbon fuels.

Chemocatalytic conversion using nanowire catalysts reduce side reactions caused on by an intermediate product while facilitating cascade reactions that lead to a desired product. In this work, metal oxide nanowires (TiO2 and WO3) were synthesised using a plasma-assisted method and metal nanoparticles (Pt and Ru) were impregnated on the as-synthesised NWs. In a high-pressure slurry batch reactor, reactions were carried out to obtain the optimal conditions for the desired product. The catalysts were characterised to reveal the catalysts-activity relationship. Various analytical techniques were used to quantify the liquid and gaseous products collected after the reactions.

The direct conversion of cellulose to C2-C3 alcohols using tungsten-based co-catalysts was enhanced even at low temperatures. X-ray photoelectrons spectroscopy (XPS) and Raman analysis show the oxygen vacancy (Ov) enrichment on the surface of Pt/TiO2 in presence of tungsten co-catalysts which improved their catalytic activity. The role of metallic platinum (Pto) was also investigated and found to have a linear relationship with the activity as follows: H2WO4 > (NH4)6H2W12O40.xH2O > H3PW12O40 . Maximum yields of 32.33% and 51.52% of ethanol and propane-2-ol at optimum temperatures of 220℃ and 250℃, respectively, were obtained with H2WO4. Catalytic reaction performed using tandem catalytic system gives a high ethanol yield of 25.56%, which is low as compared to an integrated catalytic system. Based on the experimental results, the reaction pathway is proposed which elaborates the activation and cleavage of specific C-C and C-O bonds.

Moreover, the dual functionality of tungsten oxide (WO3) nanorods as support and co-catalyst was also studied, enhances the catalytic behaviour, and the promotional study of W was studied for delivering a high yield of ethanol to 43.98% under optimum reaction conditions. The cellulose conversion was calculated to be 98.5%. The XPS study reveals the oxidation state of WO3 employing the change in catalytic activity before and after the addition of co-catalysts. The electron-deficient state of the metallic component (Ruo) is favourable for H2 adsorption on the surface, producing more active hydrogen species and thus promoting hydrogenation. As a result of these electronic understandings of Ruo and W, the reason for the higher activity of these nano synthesised Ru/WO3 compared to WO3 was concluded. Furthermore, a series of characterizations were performed to reveal the catalysts-activity relationship. Our characterization and activity test suggested that the synergistic effect of W6+ and Ruo facilitate the formation of ethanol whereas, Bronsted acid sites from W-based catalysts and Bronsted base from hot compressed water (HCW) collectively participate in the hydrolysis of cellulose and C-C cleavage of glucose to ethanol via selective hydrogenolysis of C-OH. The bond functionality was also investigated by performing reactions with various reactants under the same reaction conditions. This presentation will provide our understanding of the mechanism and kinetic correlation of the integrated cellulose-to-ethanol synthesis important for sustainable ethanol production.

Correspondence should be addressed to: sreedevi@chemical.iitd.ac.in.

Acknowledgments

The authors thankfully acknowledge funding support from TUD-IITD MFIRP project.

References

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