Hydrogenation of (—)‐α‐pinene over nickel—phosphorus/aluminum oxide catalysts prepared by electroless deposition

Abstract

Liquid-phase hydrogenation of (-)-a-pinene was investigated using a new type of amorphous nickel-phosphorus catalyst supported on aluminum oxide. The catalyst was prepared by the electroless deposition of nickel on the solid support at atmospheric pressure and moderate temperature from an aqueous solution. Two types of supports, aluminum oxide powder and pellet, were used. Electron probe micro-analysis (EPMA) indicated that the nickel profile on the aluminum oxide powder was uniform throughout the whole particle of the powdery support; however, the nickel deposition on the catalyst supported by pellet aluminum oxide exhibited an eggshell-type profile with a thickness about 8 pm. The amorphous structure of the nickel was confirmed by X-ray diffraction (XRD). The procedure by which the catalysts were prepared involved four steps: etching, sensitization, activation and deposition. The conditions employed for the sensitization, activation and deposition steps significantly affected the composition, structure, metal profile and activities of the catalysts. Etching, however, had a negligible effect on the properties of the catalysts. Very high selectivity was found for hydrogenation of (-)-a-pinene to cis-pinane.On a etudie I'hydrogenation en phase liquide du (-)-a-pinhe au moyen d'un nouveau type de catalyseur amorphe au nickel-phospore supportC sur de I'oxyde d'aluminium. Le catalyseur a CtC prtpare par un dip& de nickel sur le support solide a la pression atmospherique et B temperature modCree B partir d'une solution aqueuse par une technique non-electrique. Deux types de supports, poudre et granules d'oxyde d'aluminium, ont ete utilises. La micro-analyse par sonde des electrons (EPMA) indique que le profil du nickel sur la poudre d'oxyde d'aluminium est uniforme sur la totalit6 de la particule du support poudreux; cependant, le dCp6t de nickel sur le catalyseur supporte par l'oxyde d'aluminium sous forme de granules montre un profil en forme de coquille d'oeuf avec une epaisseur d'environ 8 pm. La structure amorphe du nickel est confirmee par la diffraction des rayons X (DRX). La procedure ayant servi a la mise au point des catalyseurs comprend quatre Ctapes: dtcapage, sensibilisation, activation et deposition. Les conditions employees pour les etapes de sensibilisation, d'activation et de deposition influent considerablement sur la composition, la structure, le profil mktallique et les activitts des catalyseurs. Toutefois, le dtcapage a un effet negligeable sur les proprittks du catalyseur. On a trouve une trks grande stlectivite pour I'hydrogenation de (-)-a-pinkne en cis-pinane.

Kinetics of the liquid-phase hydrogenation of (-)-.alpha.-pinene over electrolessly deposited nickel-phosphorus/.gamma.-alumina catalyst

“…As reported previously (Chou and KO, 1989; KO and Chou, 1993), the adsorption of (-)-apinene significantly depends on the steric factors. It was suggested that the exo rule would apply to this bridged bicyclo system as stated by Bart6k et al (1985).…”

“…It is expected that both isomerization of cis-pinane and hydrogenation of (-)-a-pinene via endo-addition to trans-pinane may occur simultaneously. On the basis of the experimental results in this study, our previous reports (Chou and KO, 1989; KO and Chou, 1993), the Horiuti and Polanyi mechanism (19341, and several reports in the literature (Siegeland Dmuchovsky, 1962;Mitsui et al, 1975;Bart6k et al, 1985), we propose that mechanism I theoretically and experimentally describes the hydrogenation of (-1-a-pinene over electrolessly-deposited Ni-Plr-Al203 catMechanism I correlates with the experimental results well. Although the Horiuti and Polanyi mechanism is not suitable for all cases (Mintsa-Eya, et al, 1983), the modified mechanism describes the experimental phenomena well.…”

“…Furthermore, the metal profile of pellet catalyst prepared by the electroless deposition method was of the egg shell type, as shown in our previous reports (Chou and KO, 1989; KO and Chou, 1993). Accordingly, the effectiveness factor for pore diffusion was about unity.…”

“…In this study, powdered catalysts were used for kinetic study. Their metal profile was near uniform (Chou and KO, 1989; KO and Chou, 1993). Accordingly, pore diffusion resistance (Zwicky and Gut, 1978) could be neglected.…”

“…In this study, a mechanism will be proposed to describe the hydrogenation catalyzed by electrolessly-deposited catalysts. The phosphorus which exists in the nickel layer of catalyst could decrease the electronic density of the neighboring nickel atom as discussed previously (Chou and KO, 1989;KO and Chou, 1993). Therefore, the nickel atoms of catalyst are classified into type A and type B nickel which are designated as the nickel atoms with deficient and sufficient electronic density, respectively.…”