H. Edward Curry-Hyde

Preparation and properties of raney copper-zinc catalyst pellets for methanol synthesis

Abstract Raney catalysts were produced by alkali leaching cylindrical pellets of a Cu-39 wt.pct.Al-17.8 wt.pct. Zn alloy to various depths using a range of leachant concentrations and temperatures. The resultant catalysts were then evaluated by measuring their activity to methanol synthesis from H 2 -5 vol.pct. CO-4 vol.pct. CO 2 at 493 K and 4500 kPa. It was found that specific surface areas decreased with increasing leach depth, the decline being more pronounced at higher alkali concentrations and at higher leach temperatures. Specific activities, measured as pellet averages, increased with leach depth until they reached a maximum and then declined. The depths at which maximal activities were achieved increased with increasing alkali concentrations and decreasing temperatures. The overall result was to yield pellets for which catalytic activities were optimal for particular leach depths. Activities comparable to industrial oxide catalyst pellets were achieved under some leach conditions

Effect of preparation procedure, oxygen concentration and water on the reduction of nitric oxide by ammonia over chromia selective catalytic reduction catalysts

Abstract The effects of preparation procedure, oxygen concentration and water on the reaction of nitric oxide and ammonia over chromia catalysts prepared by thermal treatment of chromium hydroxide have been determined. Analyses were performed using a combination of mass spectrometry, Fourier transform infrared spectroscopy and gas chromatography. Thermogravimetric and differential thermal analysis techniques show that the temperature at which transformation of amorphous chromia to the α-Cr2O3 phase occurs is dependent on the gaseous atmosphere during the heat-treatment process, and increases in the order oxygen, nitrogen and hydrogen. When heating the catalyst precursorin hydrogen, the chromia material remains amorphous for temperatures below about 420°C. Samples heated above ca. 470°C are highly crystalline. The crystallinity of the chromia material is the most significant factor in determining the activity, and selectivity, of the resulting catalysts for the NO/NH3 reaction. Amorphous chromia catalysts prepared with a two order-of-magnitude difference in ammonia addition rate show similar performances. Kenetic orders in oxygen to produce both nitrogen and nitrous oxide have been determined. Amorphous chromia shows a much higher order in oxygen for nitrogen formation than does α-Cr2O3. However, for nitrous oxide formation, the orders are approximately the same for both morphologies. Addition of 1.5% H2O vapour decreases nitric oxide and ammonia conversions over amorphous chromia for all temperatures below 275°C, whereas for α-Cr2O3, the effect varies with reaction temperature. For amorphous chromia the addition of water substantially decreases the formation of nitrous oxide.

Improvements to Raney copper methanol synthesis catalysts through zinc impregnation. II, Surface area development

The leaching of CuAl2 and a Cu-Al-Zn (43.5 wt.-%, Cu, 39.5 wt.-% Al, 17 wt.-% Zn) alloy in 6.1M sodium hydroxide and in 0.62M zincate in 6.1M sodium hydroxide has been investigated at 274 K and 303 K. The effects of leaching conditions on surface area development in the leached materials is also reported. The addition of zincate to the sodium hydroxide solution slows the leaching rate of both alloys, the greatest effect being observed for the Cu-Al-Zn alloy. The decrease in rate results in an increase in surface area. A competing process which causes rearrangement and growth of the copper crystallite limits the maximum attainable surface area, particularly at 303 K.

Improvements to Raney copper methanol synthesis catalysts through zinc impregnation: I. Electron microprobe analysis

Abstract The specific activity of a Raney Cu-ZnO-Al 2 O 3 catalyst for methanol synthesis from carbon monoxide and carbon dioxide has been found to be related to the mass of zinc per unit total area of Raney catalyst surface. This correlation hag been found to be independent of the conditions used to leach the material, although the level of zinc was found to be strongly dependent on the leaching conditions. The mass of zinc oxide in the catalytic material produced by leaching a Cu-Al-Zn alloy pellet in sodium hydroxide has been found to decrease continuously from the highest level close to the alloy/catalyst interface to the lowest level at the outer edge of the leached pellet. By leaching the alloy in a zincate rich solution the ZnO concentration profile in the leached material Cu-Al-Zn alloys can be unproved. The resulting catalysts have significantly higher specific activity which shows a strong correlation to the mass of zinc per unit total surface area. The zincate leached materials were found to have total amounts of zinc similar to the hydroxide leached materials. However, the aluminium levels were significantly lower. The high specific activity was attributed to improved contact between the copper and the ZnO which is precipitated onto the copper surface. On the basis of these results it is suggested that the active sites for methanol synthesis are at the interface between the copper and the ZnO crystallites.

Improvements to Raney copper methanol synthesis catalysts through zinc impregnation: IV. Pore structure and the influence on activity

Abstract The high activity of a Raney Cu-ZnO-Al2O3 methanol synthesis catalyst, produced by leaching Cu-Al-Zn (43.2-39-17.8 wt.-%) alloy pellets in a sodium zincate rich sodium hydroxide solution, has been compared with an industrial coprecipitated Cu-ZnO-Al2O3 catalyst. The carbon monoxide and carbon dioxide conversions for gas hourly space velocities between 11 000 h−1 and 80 000 h−1 were considerably higher for the pelleted Raney catalyst than for the coprecipitated catalyst pellets. This has been attributed to a large difference in the intra-particle mass transfer resistances of the two types of catalyst. The unique pore structure of the Raney catalyst which exhibits a well developed bimodal macro and meso pore size distribution results in low mass transfer resistances in the Raney catalyst pellets. By comparison, the coprecipitated catalyst pellets have only a small volume fraction of macro pores.

The origin of15NH3 produced from the reaction of14NH3 and15NO over vanadia-based SCR catalysts

The effects of H2O and the vanadia content of the catalyst on the formation of15NH3 during the reaction of15NO and14NH3 in the absence of O2 over V2O5-based catalysts have been determined by mass spectrometry and Fourier transform infrared spectroscopy. At 450°C, the contribution of15NH3 to the total nitrogen-containing products remains constant at about 20% for water concentrations from 0 to 1.6%. The vanadia content also has little effect on the proportion of15NH3 produced. Combination reactions producing14N15N and14N15NO consume surface oxygen species and oxygen mass balances indicate that the amount of15NH3 formed is determined by the extent of these combination reactions. Small concentrations of O2 (<300 ppm) were sufficient to prevent the formation of15NH3. The reduction of NO by H2 was also studied. Negligible amounts of NH3 were formed under dry feed conditions, whereas, in the presence of 1.6% H2O,15NH3 represents about one third of the products. A mechanism involving reaction of an adsorbed Ns species with H2O is used to account for these experimental observations.

Improvements to Raney Copper Methanol Synthesis Catalysts Through Zinc Impregnation. III. Activity Testing

Abstract Raney Cu-Zn catalysts prepared from a Cu-39 wt% Al-17.8 wt% Zn alloy and a Cu-47 wt% Al alloy by leaching in 0.62 M Na-zincate/6.1 M NaOH have been tested for activity in methanol synthesis. Comparison is made with Raney Cu-Zn catalysts prepared by NaOH leaching and to a commercial coprecipitated catalyst. The tests, conducted at 220°C, 4500 kPa and GHSV of 36000 h −1 , show the zincate leached catalysts to be up to twice as active as the other catalysts.