Methanol Synthesis Catalysts

BASF A methanol synthesis catalyst, prereduced Harshaw A methanol synthesis catalyst, prereduced Haldor A methanol synthesis catalyst, prereduced Tops0e 

A study of a methanol synthesis catalyst Is used to demonstrate the usefulness of the new pilot plant/mlnlreactor/surface analysis system. This work Is described In more detail elsewhere (7). Industrial methanol synthesis catalysts are based on Cu0/Zn0/Al20s or Cu0/Zn0/Cr203 compositions. 

The study of a CuO/ZnO/AlaOs methanol synthesis catalyst showed the working catalyst surface under our experimental conditions to consist of metallic Cu, ZnO, and Al Os. Brief exposure of such catalysts to air results In Instant formation of a few percent Cu+l. Thus, the use of a combined reactlon/analysls system as described here is absolutely essential In surface analytical studies of reactive catalyst surfaces. 

Microanalysis of a Copper-Zinc Oxide Methanol Synthesis Catalyst Precursor 

Ammonia, Hydrogen, and Methanol Production The ammonia synthesis catalyst is metallic iron promoted with AljO,. K 0. MgO. and CaO. The hydrogen-producing (methane reforming) catalyst is supported nickel. The methanol synthesis catalyst is ZnO promoted with Cr Oj or Cu(l>—ZnO promoted with CrjOl or AUOi. The respective reactions are cited as follows. 

Copper based catalysts have long been considered as the only effective methanol synthesis catalysts. However, Poutsma et al. (7) showed that palladium catalysts were active in methanol synthesis from CO-H. This latter metal had been previously considered as either almost inactive or active only for methane formation (8). Furthermore it is now known that both activity and selectivity can change drastically with the support. Vannice (9) observed that the methanation activity of a Pd/Al O was enhanced eighty and forty times compared to palladium black or Pd/SiO (or Pd/TiO ) respectively. The support effect on the selectivity was pointed out by many authors even at atmospheric pressure when the reaction temperature 

G. Meitzner, and E. Iglesia, New insights into methanol synthesis catalysts from X-ray absorption spectroscopy, Catalysis Today 53, 433-441 (1999). 

B. Gas-Induced Shape Changes in Cu/ZnO-Containing Methanol Synthesis Catalysts 

Although numerous investigations have been performed on methanol synthesis catalysts, the structure of the active catalysts, the nature of the active sites, and the reaction mechanism are still subjects of considerable controversy. 

Spencer, M.S. Waugh, K.C. Whan D.A. In "The Activity of Cu/ZnO/Al 0 Methanol Synthesis Catalysts" ACS SYMPOSIUM ON METHANOL SYNTHESIS CATALYSTS, Division of Fuel Chemistry American Chemical Society Philadelphia, 1984. 

Low Hp/CCf ratios under more moderate temperatures and pressures, with copper ased methanol synthesis catalysts possibly alkalinized yield methanol-higher alcohol mixtures (4-6) with rather high contents (5-12 wt %) of other oxygenated molecules (ketones, esters) - (7>8). 

Fig. 8. Piezo-QEXAFS spectra at the Cu K-edge recorded during reduction of a Cu/ Zn0/Al203 methanol synthesis catalyst. The recording time was 50 ms/scan, and only every 40th scan is shown (51).

Himelfarb, P. B., Simmons, G. W., Klier, K., Herman, R. G., "Precursors of the Copper-Zinc Oxide Methanol Synthesis Catalysts," J. Catal., in press. 

Fio. 6. Three-dimensional representation of in situ XRD patterns recorded during reduction of a Cu/ZnO methanol synthesis catalyst. The collection time per diagram was 60 s [adapted from Clausen et at. (32)]. 

Figure S.11. Comparison between the predictions of a micro-kinetic model and measurements on a Cu(lOO) model catalyst with a real methanol synthesis catalyst. The full line represents the ideal match between model and experiment. [Adapted from P.B. Rasmussen, P.M. Holmblad, T. Askgaard,

Figure 6.20 Quick EXAFS and XRD measurements recorded during the temperature programmed reduction of copper in a Cu/Zn0/Al203 methanol synthesis catalyst. The disappearance and appearance of peaks with increasing temperature in the series of EXAFS spectra corresponds to the conversion of oxidic to metallic copper. The intensity of the relatively sharp peak around 9040 eV, indicative of Cu metal, clearly illustrates the kinetics of the reduction process, as does the intensity of the (111) reflection of Cu metal in the XRD spectra (adapted from Clausen 44J).

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

R. G. Herman et al. (8) studied these catalyst systems In great detail and suggested a Cu-fl solution In ZnO as active phase where Cu- - non-dlssoclatlvely chemisorbs and activates CO and ZnO activates H2. In the range of 15 to 85Z CuO In the catalyst, up to 16% Cu+1 became dissolved In the ZnO (9) and Cu+1 has been widely accepted as active site (10). Recently, however, Raney Cu-Zn catalysts have been shown to be very active methanol synthesis catalysts (11). The active component for these Raney catalysts was found to be metallic Cu with an activity maximum at 97 wt% Cu (12). 

---