Novel bionanocatalysts for green chemistry applications

Abstract

Desulfovibrio desulfuricans have been known to synthesize good catalysts in a number of industrially and environmentally relevant reactions but the underlying reasons and/or mechanisms for such catalysis have largely remained elusive. This study has shown that in addition to nanoparticle (NP) size, the catalytic properties of D. desulfuricans is hinged on several factors such as the textural surface of the bacterial support, binding mechanism to surface functional groups (amine, carboxyl, phosphoryl and sulfuryl groups) and the crystal structure of the resulting catalyst NPs. In this study, various characterization techniques: AFM, EDX, SEM, HAADF-STEM, HRTEM, XRD and XPS and catalytic hydrogenation of soybean oil. The concept of intracellular trafficking of palladium into the cells of both Gram-negative (Desulfovibrio desulfuricans) and Gram-positive (Bacillus benzeovorans) bacteria was pioneered against previously known extracellular NP deposition. The membrane integrity and membrane potentials of “palladized” cells (‘bio-Pd’) were found to be retained through flow cytometry analysis. Bio-supported bimetallic (bio-Pd/Pt) catalyst from D. desulfuricans and B. benzeovorans demonstrated comparable catalytic properties to a commercial catalyst (Ni-Mo/Al$_2$O$_3$) as a potential ‘green’ alternative. Generally, the extent of viscosity reduction was: 98.7% (thermal), 99.2% (bio-NPs) and 99.6% (Ni-Mo/Al$_2$O$_3$) below 1031 mPa.s of the feed heavy oil. Also the bimetallic bio-NPs produced an increment of ~2$^o$ in API (American petroleum institute) gravity (~9.1$^o$) than monometallic (~7.6$^o$) on average while the API gravity using thermal was lower (6.3$^o$) while that of a commercial catalyst was 11.1$^o$. Finally, the concept of tandem (one-pot) catalysis was pioneered as a potential platform for the remediation of chlorinated benzenes