Palladium Nanoparticles Supported on Magnesium Hydroxide Fluorides: A Selective Catalyst for Olefin Hydrogenation

Abstract

A one‐pot synthesis of palladium nanoparticles supported on magnesium hydroxide fluoride has been performed with the fluorolytic sol–gel method. The prepared catalysts were characterized by using various physicochemical techniques. The sol–gel method led to high surface area (>135 m2 g−1), mesoporous catalysts (pore volume=0.19–0.23 cm3 g−1, pore diameter=3–5 nm) with uniformly dispersed palladium nanoparticles approximately 2 nm in diameter on the surface. The catalysts synthesized by using different concentrations of aqueous hydrofluoric acid exhibited changing surface and acidic properties. Very high dispersion of palladium on magnesium fluoride (47 %) was obtained with 1 wt % palladium loading. The catalysts were used for hydrogenation of various olefins in the presence of other organic functionalities at room temperature and atmospheric hydrogen pressure. Various substituted olefins were hydrogenated with almost 100 % conversion and selectivity. The catalysts were recycled efficiently over five cycles without appreciable loss in catalytic activity. There was no palladium leaching under the reaction conditions, which was confirmed by inductively coupled plasma atomic emission spectroscopy analysis. Activation of olefin on the catalyst surface could not be observed by in situ FTIR studies, indicating facile activation of hydrogen on the palladium supported on magnesium hydroxide fluoride.

Palladium Supported on Fluorinated Magnesium Hydroxide: An Efficient Catalyst for Hydrogenation under Ambient Conditions

“…The diffraction pattern of the catalyst Pd‐MgF 2‐x (OH) x is shown in Figure . The XRD pattern matched very well with the diffraction pattern of magnesium hydroxide fluoride phase reported previously . The peaks observed at 2θ=27.3° (110), 35.2° (101), 40.4° (111), 43.8° (201), 53.5° (211), 56.2° (220), 60.7°, 68.1° (301), 77.4°, and 87.4° are the characteristics of the magnesium fluoride phase.…”

“…Hence in the present case, the adsorption of nitrobenzene can be explained on the Lewis acidic centre in the MgF 2‐x (OH) x support with chelation of ONO group to Mg +2 centre as shown in Figure (I). Previously the facile activation of hydrogen on Pd centre in Pd‐MgF 2‐x (OH) x at room temperature and atmospheric pressure has been shown in hydrogenation of styrene using Pd‐MgF 2‐x (OH) x by our group ,…”

“…Addition of palladium acetate in the same pot after dissolution of magnesium hydroxide led to the simultaneous impregnation of palladium acetate during precipitation of MgF 2‐x (OH) x forming Pd‐MgF 2‐x (OH) x as final catalyst. This method is much simpler compared to fluorolytic sol‐gel method developed previously . This method does not need inert atmosphere as well as critical control of reaction parameters during synthesis.…”

“…The catalytic activity of the Pd‐MgF 2‐x (OH) x catalyst was tested for hydrogenation of styrene to compare the performance with similar catalyst composition (Pd‐MgF 2 ‐40) prepared by flourolytic sol‐gel method (Scheme , Table ). PdMgF 2 ‐40 catalyst was prepared by sol‐gel method using 40% aqueous HF for fluorolysis of Mg methoxide as reported in our previous work . In present case 40% aqueous HF is used for catalyst preparation, hence the catalytic activity is compared with PdMgF 2 ‐40 catalyst.…”

“…Palladium supported on magnesium fluoride Pd‐MgF 2‐x (OH) x catalyst prepared in our group following fluorolytic sol‐gel route has shown very high efficiency for selective hydrogenation of various olefins under ambient conditions . The fluorolytic sol‐gel route provides mesoporous material with very high surface area and tunable acidity.…”