Efficient hydrogenation of p-chlorophenol and Cr(VI) driven by hydrogen rich balls over Pd/C catalysts

Catalytic hydrogenation can selectively destabilize and detoxify specific contaminants in water. Herein, to explore safer and more efficient hydrogen sources, hydrogen rich balls (HRBs) were researched and applied for hydrogenating p-chlorophenol and Cr(VI) over Pd/C catalyst. The results showed that HRBs can realize the sustained release of H₂ by replacing the hydrogen in water, and generate the refined (micro/nano-sized) H₂ bubble, which effectively improves the adsorption and activation effectively of H₂ molecules on Pd/C catalyst, and the hydrogen atoms utilization efficiency during p-chlorophenol hydrodechlorination is as high as 3.5 %. Continuous flow experiments showed that rapid removal of p-chlorophenol with different concentrations could be achieved by adjusting the flow rate. Moreover, the high-toxic Cr(VI) was successfully reduced to the low-toxic Cr(III) in an appropriate pH range. This research is of far-reaching significance for realizing the detoxification of environmental pollutants and promoting the development of hydrogen economy.

Defining the Qualities of High-Quality Palladium on Carbon Catalysts for Hydrogenolysis

Palladium-catalyzed hydrogenolysis is often the final step in challenging natural product total syntheses and a key step in industrial processes producing fine chemicals. Here, we demonstrate that there is wide variability in the efficiency of commercial sources of palladium on carbon (Pd/C) resulting in significant differences in selectivity, reaction times, and yields. We identified the physicochemical properties of efficient catalysts for hydrogenolysis: (1) small Pd/PdO particle size (2) homogeneous distribution of Pd/PdO on the carbon support, and (3) palladium oxidation state are good predictors of catalytic efficiency. Now chemists can identify and predict a catalyst's efficiency prior to the use of valuable synthetic material and time.

Catalytic Hydrodechlorination of Chlorophenols in a Continuous Flow Pd/CNT-Ni Foam Micro Reactor Using Formic Acid as a Hydrogen Source

Catalytic hydrodechlorination (HDC) has been considered as a promising method for the treatment of wastewater containing chlorinated organic pollutants. A continuous flow Pd/carbon nanotube (CNT)-Ni foam micro reactor system was first developed for the rapid and highly efficient HDC with formic acid (FA) as a hydrogen source. This micro reactor system, exhibiting a higher catalytic activity of HDC than the conventional packed bed reactor, reduced the residence time and formic acid consumption significantly. The desired outcomes (dichlorination >99.9%, 4-chlorophenol outlet concentration <0.1 mg/L) can be obtained under a very low FA/substrate molar ratio (5:1) and short reaction cycle (3 min). Field emission scanning electron microcopy (FESEM) and deactivation experiment results indicated that the accumulation of phenol (the main product during the HDC of chlorophenols) on the Pd catalyst surface can be the main factor for the long-term deactivation of the Pd/CNT-Ni foam micro reactor. The catalytic activity deactivation of the micro reactor could be almost completely regenerated by the efficient removal of the absorbed phenol from the Pd catalyst surface.

Rapid, highly efficient and stable catalytic hydrodechlorination of chlorophenols over novel Pd/CNTs-Ni foam composite catalyst in continuous-flow

A novel Pd/CNTs-Ni foam composite catalyst was developed for catalytic hydrodechlorination of chlorophenols by using CNTs-Ni foam as support. Characterizations including FESEM, TEM/HRTEM, HAADF-STEM and element mapping revel that the composite catalyst with 2 wt.% Pd loading possesses high porous micro-network structure and high dispersed active Pd nanoparticles (5.81 nm) on CNTs surface. The HDC of chlorophenols over Pd/CNTs-Ni foam composite catalyst has been studied in continuous-flow packed bed reactor. This packed bed reactor system with Pd/CNTs-Ni foam composite catalyst, presented the very short reaction cycle (22-74 s), high efficiency (dechlorination > 99.95%) and excellent catalytic stability during HDC in continuous-flow, making it to be a promising candidate for the HDC of wastewater containing highly toxic chlorinated organic pollutants and other Pd catalyzed hydrogenation reactions.