David M. Minahan

Higher alcohol synthesis reaction study using K- promoted ZnO catalysts. III

Recent results indicate that modified high- temperature, high- pressure, Zn/Cr spinel methanol synthesis catalysts consist primarily of ZnO at the catalyst surfaces. Nonpromoted and K- promoted ZnO powders, therefore, were tested for methanol and isobutanol production using a 1:1 H2 and CO syngas feedstream at two operating pressures (6.9 and 10.3 MPa) and two reactor bed temperatures (400 and 440°C). No isobutanol formation occurs over the nonpromoted ZnO. The highest isobutanol production is obtained using a 1 wt% K-containing ZnO catalyst while operating the reactor at 440°C and 10.3 MPa, but the greatest hydrocarbon byproduct rate also is obtained under these conditions. Although the isobutanol product rates are lower than the best values presented in the literature, the product rate of isobutanol formation is limited by a lower surface area of the promoted ZnO catalysts in comparison to the Zn/Cr spinel catalysts. The ratio of the BET surface areas of the K/ZnO catalysts to the surface area of an alkali-modified, commercial Zn/Cr spinel catalyst is approximately 0.23. Comparison of the catalysts on a surface area basis could result in the promoted ZnO samples performing better than the alkali- promoted Zn/Cr spinel catalysts. Most importantly, this study demonstrates that the promoted ZnO is the active catalyst phase for this reaction and that the spinel structure is not required for high activity.

Higher-alcohol synthesis reaction study V. Effect of excess ZnO on catalyst performance

Abstract A nonpromoted, K-promoted, and Cs-promoted 1 : 1 Zn/Cr spinel as well as K- and Cs-promoted Zn/Cr spinel catalysts containing excess ZnO were tested for higher alcohol synthesis (HAS) using a syngas feedstream (1 : 1 CO : H 2 ). Two reactor operating pressures, 1000 and 1500 psig, and two reactor bed temperatures, 400 and 440°C, were used in order to determine the influence of these operating parameters, and the effects of promotor concentrations and excess ZnO on the product stream composition. Of the catalysts tested, the 3 wt% Cs/Zn/Cr catalyst with excess ZnO yields the highest isobutanol production rate of 171 g/kg h at 440°C and 1500 psig. Although lower methanol-to-isobutanol mole ratios were attained, this catalyst yields a ratio of 1.4 which is nearly ideal for downstream synthesis of methyl tertiary-butyl ether (MTBE). Superior performance is achieved using Cs as the promotor on the Zn/Cr spinels in comparison to the K promotor. Lower hydrocarbon production rates and corresponding increased selectivities to total alcohols, however, are obtained using K as the promotor of the 1 : 1 Zn/Cr spinel catalysts while Cs is more effective in reducing the hydrocarbon production in the presence of excess ZnO. The addition of excess ZnO to the Cs-promoted catalyst enhances not only the isobutanol rate but also results in increased selectivity, lower hydrocarbon production rates and lower methanol-to-isobutanol mole ratios at the higher Cs loadings. Higher isobutanol production rates are also obtained over the K-promoted Zn/Cr spinels containing excess ZnO in comparison to the K-supported 1 : 1 Zn/Cr spinels if 3 wt% or greater K addition is employed, but higher hydrocarbon production rates result in lower selectivities to the desired alcohol products.

An efficient catalyst for the production of isobutanol and methanol from syngas. XI. K- and Pd-promoted Zn/Cr/Mn spinel (excess ZnO)

A 2.25 wt% K‐ and 6.0 wt% Pd‐promoted Zn/Cr/Mn spinel (excess ZnO) higher alcohol synthesis (HAS) catalyst has been tested for the production of isobutanol and methanol at 440°C and 1500 psig. An isobutanol production rate of 179 g kg−1 h−1, a methanol‐to‐isobutanol mole ratio of 1.3 and a total alcohol rate of 304 g kg−1 h− are attained. This ratio is slightly higher than the desired value of 1.0 for MTBE production. These results are superior to others presented in the literature thus far. Surface characterization data indicate that the near‐surface region of the catalyst consists primarily of ZnO and K. Pretreating the catalyst in a reductive environment similar to that given to the catalyst before reaction tests, causes an enrichment of the K promoter at the surface. The product stream composition does not significantly change during five days of testing.

ION-BEAM CHARACTERIZATION OF ALUMINA-SUPPORTED SILVER CATALYSTS USED FOR ETHYLENE EPOXIDATION

Abstract α-alumina-supported Ag epoxidation catalysts have been examined using ion scattering spectroscopy (ISS) and scanning electron microscopy (SEM). This combination of techniques provides a means of relating surface morphology and outermost atomic layer composition as the catalyst ages. This is of particular importance in characterization studies of catalysts because the catalytic reaction occurs at the outermost atomic layer and the chemical and morphological changes are closely related. The fresh catalyst promoted with Cs consists of a fairly uniform coating of Ag over the planar α-alumina surface. With aging the activity first increases and then decreases corresponding to changes in the Ag structure to a globular film and then to well-defined large crystallites which do not appear to interact strongly with the α-alumina support. The ISS spectrum obtained from the aged catalyst exhibits a large Na feature indicating that Na migration to the surface may play a role with regard to aging and loss of activity. The presence of the Cs promotor results in a more uniform distribution of the Ag across the α-alumina support surface for the fresh catalyst.

Formation and detection of subsurface oxygen at polycrystalline Pd surfaces

An ion-sputtered, oxygen-exposed, polycrystalline palladium surface has been studied using ion scattering spectroscopy (ISS) before and after exposures to H2 and CO. A room-temperature exposure to O2 for 1 min at 1 × 10−7 Torr does not yield chemisorbed oxygen in the outermost layer of atoms according to the ISS data. However, subsequent exposure to H2 or CO induces subsurface oxygen formed during the Oa exposure to migrate to the surface under a chemical driving force and populate the outermost atomic layer where it is detected by ISS. This study demonstrates that a reductive treatment can increase the oxygen content of a surface and provides a useful method for examining subsurface oxygen.

Potassium Dichromate by XPS

XPS data were collected from a pressed potassium dichromate powder. A small amount of contamination is present in hydrocarbon and carbide states. A small amount of subsurface dissolved O is also apparent. The spectra obtained from the as-received powder indicate that single states of K and Cr are present and therefore these data can be considered to be characteristic of K2Cr2O7.

Potassium Chromate by XPS

XPS data were collected from a pressed potassium chromate powder. The spectra obtained from the as-received powder indicate that single states of K, Cr, and O are present due to K2CrO4. A small amount of C contamination is present in hydrocarbon and carbide forms. Therefore these data can be considered to be characteristic of K2CrO4.

Reaction and surface characterization study of Zn/Cr-based higher-alcohol synthesis catalysts X: Effects of excess promoter loading on surface chemistry

Promoter loading level significantly affects the catalytic behavior of Zn/Cr spinel higher alcohol synthesis (HAS) catalysts. In this study a 5.9 wt.% Pd-promoted Zn/Cr spinel with a 5 and 7 wt.% K promoter have been tested and compared. At 1500 psig and 400°C, the catalyst containing 5 wt.% K results in the production of slightly more butanol, less methanol and more hydrocarbons. Using ion scattering spectroscopy and X-ray photoelectron spectroscopy, differences are found between the two catalyst surfaces which must be responsible for the differences in catalytic behavior.

Factors influencing deactivation of Cs-promoted, α-alumina-supported silver, ethylene-epoxidation catalysts

Abstract The various factors relating to deactivation of an α-alumina supported, Cs-promoted, Ag ethylene epoxidation catalyst has been examined before and after aging in a Bertz reactor using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS). The SEM micrographs indicate that the fresh catalysts consist of a fairly uniform coating of Ag over the alumina and sintering occurs during aging. The ELS data indicate that the Ag is in metallic form before and after aging while angle-resolved AES data indicate that the near-surface region of the Ag becomes enriched in oxygen during aging. The Cl content at the surface also increases during aging due to adsorption of the moderator.