Comparison of degradation features of lignin to phenols over Pt catalysts prepared with various forms of carbon supports

Abstract

Soda lignin separated from wheat straw was successfully depolymerized to produce a phenol-rich oil fraction over various carbon-supported platinum (Pt) catalysts. Three different supports (mesoporous carbon (STC), porous carbon (TC), and microporous carbon (DC)) were prepared; 5 wt% Pt on commercial activated carbon (Pt/C) was also used as a comparison. The surface characterizations of the catalysts were examined by FE-SEM, BET, XRD, XPS and HR-TEM. The Pt/C and Pt/STC proved to be superior catalysts for producing high yields of lignin-oil (Pt/C: 79.9 wt% and Pt/STC: 79.4 wt%) with low amounts of char (Pt/C: 4.2 wt% and Pt/STC: 7.6 wt%) compared to the other catalysts. This is due to the fine dispersion of Pt (i.e., higher BET surface area) on these carbon supports. In addition, we found a high correlation between the BET surface area (Pt dispersion) and the molecular weight of the lignin-oil. The amounts of monomeric phenol compounds, which are mainly composed of 4-ethlyphenol, 4-methylguaiacol, and 4-propylguaiacol, were also higher with Pt/C (90.92 mg g⁻¹ of lignin) and Pt/STC (78.06 mg g⁻¹ of lignin) compared to the other samples.