An efficient reduction of unsaturated bonds and halogen-containing groups by nascent hydrogen over Raney Ni catalyst

Water oxidation couples to electrocatalytic hydrogenation of carbonyl compounds and unsaturated carbon–carbon bonds by nickel

Artificial photosynthesis, an umbrella term, is a chemical process that biomimetics natural photosynthesis. In natural photosynthesis, electrons from the water-oxidation reaction are used for carbon dioxide reduction. Herein, we report the reducion of aldehydes and ketones to corresponding alcohols in a simple undivided cell. This reaction utilized inexpensive nickel foam electrodes (1 cm2) and LiClO4 (0.05 M) as a commercially accessible electrolyte in an aqueous medium. Under electrochemical conditions, a series of alcohols (21 examples) produces high selectivity in good yields (up to 100%). Usage the current method, 10 mmol (1060 mg) of benzaldehyde is also successfully reduced to benzyl alcohol (757 mg, 70% isolated yield) without any by‑products. This route to alcohols matched several green chemistry principles: (a) atom economy owing to the use of H2O as the solvent and the source of hydrogen, (b) elimination of the homogeneous metal catalyst, (c) use of smooth reaction conditions, (d) waste inhibition due to low volumetric of by-products, and (e) application of safe EtOH co-solvent. Moreover, the ability of the system to operate with alkyne and alkene compounds enhanced the practical efficiency of this process.

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.

Liquid-phase hydrodechlorination of trichloroethylene driven by nascent H2 under an open system: Hydrogenation activity, solvent effect and sulfur poisoning

Hydrodechlorination is a promising technology for the remediation of water body contaminated with trichloroethylene (TCE). In this work, the liquid-phase hydrogenation of TCE by Raney Ni (R-Ni) and Pd/C under an open system have been studied, in which nascent H₂ (Nas-H₂) generated in situ from the cathode acted as a hydrogen source. Experimental results showed that TCE was completely eliminate from the solution through the synergistic effects of hydrodechlorination and air flotation due to the formation of continuous micro/nano-sized Nas-H₂ bubbles from the cathode. Furthermore, the effects of inorganic anions and organic solvents on R-Ni and Pd/C hydrogenation activity were investigated, respectively. The results showed that NO₃^- and acetonitrile can form a competitive reaction with TCE; Sulfur with lone-pair electrons will cause irreversible poisoning to these two catalysts, and have a stronger inhibitory effect on Pd/C. This work helps to realize the separation of volatile halogenated compounds from water environment and provides certain data support for the choice of catalyst in the actual liquid-phase hydrogenation system.

Raney nickel coupled nascent hydrogen as a novel strategy for enhanced reduction of nitrate and nitrite

Raney nickel (R-Ni) is a cost-effective hydrogenation catalyst, and nascent hydrogen (Nas-H₂) generated in situ on the cathode trends to more reactive than commercial hydrogen (Com-H₂). In the present work, nitrate and nitrite (NO_X^-) reduction via R-Ni/Nas-H₂ catalytic system was investigated. The results show that hydrogenation of NO_X^- (C₀ = 3.0 mM) follows pseudo-first-order reaction kinetics with kinetic constants of 5.18 × 10^-2 min^-1 (NO₃^-) and 6.46 × 10^-2 min^-1 (NO₂^-). The saturation demand for Nas-H₂ is only 0.8 mL min^-1 at a fixed R-Ni dosage of 1.0 g L^-1. The experiments reveal that both Nas-H₂ and hydrogen adatoms (H_ads∗) can drive the reduction of NO_X^-. The improved reduction ratios of NO_X^- are attributed to two aspects: (1) the micro/nano-sized Nas-H₂ bubbles exhibits increased reactivity due to the fine dispersion of the hydrogen molecules; (2) the alkaline environment formed by the cathode positively maintain R-Ni activity, thus, Nas-H₂ bubbles were more readily activated to generate powerful H_ads∗. The results give insight into NO_X^- hydrogenation via introducing fine hydrogen resource, and can develop an efficient catalytic hydrogenation technique without noble metals.