Pd-NCQD composite confined in SBA-15 as highly active catalyst for aqueous phase catalytic hydrodechlorination of 2,4-dichlorophenoxyacetic acid

Abstract

A composite consisting of Pd particles and N-doped carbon quantum dots (NCQDs) confined in mesoporous SBA-15 (Pd-NC@SBA-15) was prepared. For comparison, Pd catalysts supported on SBA-15 (im-Pd/SBA-15), NCQDs modified SBA-15 (im-Pd/NC-SBA-15) and N-doped carbon nanotubes (Pd/NCNTs) were prepared using the impregnation method. The catalysts were characterized and the aqueous phase catalytic hydrodechlorination (HDC) of 2,4- dichlorophenoxyacetic acid (2,4-D) was investigated. Characterization results showed that Pd-NC@SBA-15 had a higher Pd dispersion and more homogeneous Pd particle distribution than other catalysts. Additionally, the presence of NCQDs led to increased content of positively charged Pd in Pd-NC@SBA-15. As a result, Pd-NC@SBA-15 exhibited a much higher catalytic activity. Furthermore, the turnover frequency value of the Pd-NC@SBA-15 catalyst increased with Pdn+ content and remained identical at Pdn+/Pd0 ratio above 1.20. The HDC of 2,4-D on Pd-NC@SBA-15 proceeded via both stepwise and concerted pathways and the stepwise dechlorination pathway was predominant. The present study highlights that substantial enhancement of the catalytic activity can be achieved by rational NCQDs modification of Pd based catalysts for the aqueous phase catalytic removal of pollutants.