Pt supported on ordered microporous carbon as highly active catalyst for catalytic hydrodeiodination of iodinated X-ray contrast media

摘要

In this study, Pt catalysts supported on zeolite templated carbon (Pt/ZTC) were prepared by in-situ chemical vapor deposition using Pt exchanged Y zeolite as the template. For comparison, Pt catalysts supported on zeolite templated carbon (ZTC) and commercial activated carbon (AC) were prepared using the impregnation method. The liquid phase catalytic hydrodeiodination of two iodinated X-ray contrast media (ICM, i.e., diatrizoate and iopamidol) was investigated on the catalysts. The catalysts were characterized by X-ray diffraction, N-2 adsorption desorption isotherms, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy and zeta-potential measurement. The results showed that Pt/ZTC catalysts prepared by in situ chemical vapor deposition (CVD) under varied reaction conditions were good replicas of Y zeolite in structure. Compared with the catalysts prepared by the impregnation method, Pt/ZTC had a higher Pt dispersion and more homogeneous Pt distribution. Increasing CVD temperature resulted in Pt particle growth in Pt/ZTC. The catalytic hydrodeiodination of diatrizoate and iopamidol proceeded via a sequential deiodination pathway, and followed the Langmuir-Hinshelwood model, reflecting that the conversion of adsorbed ICM was the rate controlling step. Additionally, more effective conversion of iopamidol was observed than that of diatrizoate on Pt/ZTC. Furthermore, Pt/ZTC prepared at higher CVD temperature exhibited lower catalytic activities for the hydrodeiodination of diatrizoate and iopamidol. Solution pH markedly impacted the catalytic ICM conversion, and enhanced hydrodeiodination was observed with the increase of pH. As for catalyst reuse, Pt/ZTC remained about 80% of initial activity after 4 reuse cycles, exhibiting much higher stability than the catalyst prepared by the impregnation method. The present findings highlighted the Pt/ZTC catalysts prepared by in-situ CVD as highly active and stable catalysts for the removal of halogenated organic pollutants by catalytic hydrogenation.