Effect of Carbon Support, Capping Agent Amount, and Pd NPs Size for Bio-Adipic Acid Production from Muconic Acid and Sodium Muconate

Sofia Capelli,Nikolaos Dimitratos,Davide Motta,Carlo Pirola,Alberto Villa,Claudio Evangelisti,Laura Prati

doi:10.3390/nano10030505

Abstract

The effect of support, stabilizing agent, and Pd nanoparticles (NPs) size was studied for sodium muconate and t,t-muconic acid hydrogenation to bio-adipic acid. Three different activated carbons (AC) were used (Norit, KB, and G60) and carbon morphology did not affect the substrate conversion, but it greatly influenced the adipic acid yield. 1% Pd/KB Darco catalyst, which has the highest surface area and Pd surface exposure, and the smallest NPs size displayed the highest activity. Furthermore, the effect of the amount of the protective agent was studied varying metal/protective agent weight ratios in the range of 1/0.00–1/1.20, using KB as the chosen support. For sodium muconate reduction 1% Pd/KB_1.2 catalyst gave the best results in terms of activity (0.73 s−1), conversion, and adipic acid yield (94.8%), while for t,t-muconic acid hydrogenation the best activity result (0.85 s−1) was obtained with 1% Pd/KB_0.0 catalyst. Correlating the results obtained from XPS and TEM analyses with catalytic results, we found that the amount of PVA (polyvinyl alcohol) influences mean Pd NPs size, Pd(0)/Pd(II) ratio, and Pd surface exposure. Pd(0)/Pd(II) ratio and Pd NPs size affected adipic acid yield and activity during sodium muconate hydrogenation, respectively, while adipic acid yield was related by exposed Pd amount during t,t-muconic acid hydrogenation. The synthesized catalysts showed higher activity than commercial 5% Pd/AC.

Highlights

Nowadays many companies make efforts to convert the old traditional chemical productions to a more sustainable and environmentally friendly manufacturing following the concept of sustainable process, green chemistry, and circular economy
Correlating the results obtained from X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses with catalytic results, we found that the amount of polyvinyl alcohol (PVA) influences mean Pd NPs size, Pd(0)/Pd(II) ratio, and Pd surface exposure
A series of 1% PdPVA/activated carbons (AC) catalysts were synthesized by sol-immobilization method and characterized by means of BET, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS)

Summary

Introduction

Nowadays many companies make efforts to convert the old traditional chemical productions to a more sustainable and environmentally friendly manufacturing following the concept of sustainable process, green chemistry, and circular economy. Considering catalytic reactions, capping agents (i.e., stabilizers) are considered to have a great impact on the performance of metal NPs due to the hindered access of the substrate on the catalyst surface and their chemical nature [19,20]. The catalytic performance of the designed catalysts was evaluated for the hydrogenation reactions of trans,trans-muconic acid (t,t-MA), and sodium muconate (Na-Muc) (Figure 1). Since the operating conditions were already optimized in a previous study [27], we decided to perform the reaction using 1% PdPVA/AC catalysts prepared by sol-immobilization method keeping constant the reaction temperature (50 ◦C), hydrogen pressure (1 bar), substrate concentration (0.014 M), and metal to substrate ratio (1/200 molPd/molsubstrate). Initial activity was evaluated considering the amount of catalyst used for each test, the conversion, and the time of the reaction (Equation (4)). Aldrich) was used to compare the results in terms of activity

Catalyst Characterization

Support Effect

Influence of PVA Amount

Conclusions