Jan B. Friedrich

Methanol synthesis over Raney copper-zinc catalysts: I. Activities and surface properties of fully extracted catalysts

The activity of fully extracted Raney copper-zinc catalysts for the methanol synthesis reaction, and the associated physical and chemical properties of these catalysts, have been examined. The Raney catalysts were prepared by leaching a series of AlCusZn alloys containing approximately 50 wt% Al and differing CuZn ratios with aqueous NaOH until complete reaction had taken place. Hydrogenation of a mixture of carbon monoxide and carbon dioxide showed that Raney catalysts prepared from alloys containing approximately 50 wt% Al, 30–36 wt% Cu, and 14–20 wt% Zn had the greatest activity for methanol synthesis. The active component for these Raney catalysts was found to be metallic copper and the activity exhibited a maximum for catalysts containing approximately 97 wt% copper. The residual zinc in these catalysts was found to provide a promotional effect to catalytic activity. The surface areas of the catalysts increased from 17 to 39 m2g−1 with increasing zinc content of the precursor alloy. The catalysts exhibited a narrow pore size distribution with the pore radius decreasing with increasing alloy zinc level. Carbon monoxide and hydrogen adsorption were used to determine the nature of the catalyst surface.

Methanol synthesis over Raney copper-zinc catalysts: II. Activities and surface properties of a partially leached alloy

Catalysts prepared by the caustic leaching of an alloy containing 36 wt% Cu, 15 wt% Zn, and 49 wt% Al for various periods of time have been shown to have high activities for methanol synthesis. The activity passes through a maximum with time of leaching and is related to both increased surface area and concentration of zinc oxide on the catalyst surface. It has been established that the presence of zinc oxide increases the activity of Raney copper for the methanol synthesis reaction.

Caustic Leaching of Al‐Cu‐Zn Alloys to Produce Raney Catalysts I . Morphological Development

The leaching behavior in aqueous of Al‐Cu‐Zn alloys containing 50 weight percent (w/o) Al has been examined and interpreted in terms of alloy phase constitution. Alloys containing approximately 0, 5, 10, 17, 26, 33, and 50 w/o Zn having quenched structures consistent with the ternary phase diagram were partially leached and the product material examined metallographically. In all cases a sharply defined interface developed between the as yet unaffected alloy and the reaction product layer. This layer was of uniform thickness. The principal reaction product was porous copper (containing small amounts of zinc and aluminum) which resulted from leaching of the alloy phase. The microstructure of the alloy was reproduced in the reaction product, suggesting that the mechanism is one of selective dissolution.

DEVELOPMENT OF RANEY-TYPE LOW TEMPERATURE METHANOL SYNTHESIS CATALYSTS†

Catalysts prepared by caustic leaching of Cu—Zn—Al alloys are shown to have activities greater than those of a commercial copper-based catalyst. Complete leaching of alloys containing 50 wt.% aluminium, with between 0 and 50 wt.% copper, and the balance zinc produced catalysts having a wide range of activities. The most active catalysts for methanol production were produced from alloys containing from 10 to 20 wt.% zinc. The activities of catalysts prepared by the partial leaching of an alloy containing approximately 36% copper, 15% zinc and 48% aluminium were shown to pass through a maximum at a leaching time of 2.75 hours. This catalyst had more than double the activity of a commercial catalyst al reaction conditions similar to those employed industrially.

OPTIMISATION OF THE PREPARATION OF RANEY COPPER-ZINC CATALYSTS FOR METHANOL SYNTHESIS

The large number of variables involved in the preparation of Raney copper-zinc catalysts for methanol synthesis were screened by statistical methods using a Plackett-Burman screening design. Three important variables, leach reaction temperature, leach digestion temperature and leach digestion time were further investigated using a central composite design. It was found that active Raney copper-zinc catalysts were produced using high (348-358 K) extraction temperature, low (298-318 K.) digestion temperature and long (70-80 min) digestion time