Influence of lanthanum on the surface structure and carbon monoxide hydrogenation activity of supported cobalt catalysts

Abstract

X-ray photoelectron spectroscopy (ESCA or XPS), X-ray diffraction (XRD), Raman spectroscopy, H2 chemisorption, and gravimetric analysis have been used to characterize three series of La/Al303 and CoLa/Al203 catalysts. CoLa/Al2G3 catalysts were prepared by two methods: impregnation of La first followed by Co (designated "CoLay") and impregnation of Co first followed by La (designated "LayCo"). The information obtained from surface and bulk characterization has been compared with CO hydrogenation activity and selectivity of the supported Co/A1203 catalysts. For CoLay catalysts with low La loadings (La/Al atomic ratio <0.026), the presence of La had little effect on the structure or CO hydrogenation activity. However, the selectivity to higher hydrocarbons and olefinic products increased with increasing La content. For CoLay catalysts with higher La loadings, Co304 is suppressed in favor of an amorphous dispersed La-Co mixed oxide. ESCA and H2 chemisorption indicated higher dispersion of the metallic cobalt phase for high La loadings. The turnover frequency (TOF) for CO hydrogenation decreased dramatically for high La loadings. This has been correlated to the decrease in the amount of Co304 present in the La-rich catalysts. Catalysts prepared by reverse impregnation (LayCo) showed little evidence of La-Co interaction. No significant variation in reducibility or cobalt metal dispersion was observed. Lanthanum addition had little effect on the TOF for CO hydrogenation or the selectivity to olefinic products and higher hydrocarbons.

Carbon Dioxide Reforming of Methane over Ni Catalysts Supported on Al2O3 Modified with La2O3, MgO, and CaO

“…The Ni-La-1 and Ni/h-Al 2 O 3 catalysts showed similar TPR patterns, i.e., a broad peak at peak maximum of about 923 K and a small shoulder peak at peak maximum of about 1,073 K. Furthermore, the lower reduction peak of the Ni/h-Al 2 O 3 catalyst was sharper than that of the Ni-La-1 catalyst, which can be explained as the effect of La 2 O 3 in the catalysts. The broad peak could be attributed to the reduction of complex NiO species having strong interactions with the support while the small shoulder peak was assigned to the reduction of the highly dispersed NiAl 2 O 4 species as discussed in other investigations [31,[38][39][40][41].…”

“…It is also well established that the stabilization effect is closely related to the phase of the loaded La 2 O 3 , i.e., highly dispersed La species, LaAlO 3 and lanthanum b-Al 2 O 3 , which are determined by sintering temperature and La 2 O 3 loading [32,33,35,40], although the mechanism of the stabilization effect is still ambiguous and has not been fully understood. From the BET results La-1 and Ni-La-1 samples with a La/Al ratio of 0.02 showed the highest surface area among the samples tested.…”

Fischer–Tropsch Synthesis on Lanthanum Promoted Co/TiO2 Catalysts

“…Adachi et al [12] reported that lanthanum addition could promote the activity of Co/SiO 2 catalysts by the agglomeration of cobalt. Ledford et al [13] reported that there was little effect on the support structure or CO hydrogenation activity for Co/Al 2 O 3 catalysts with lanthanum promotion at low contents, while a decrease in TOF was observed at higher levels of lanthanum promotion. Vada et al [14] showed that, with increasing La 2 O 3 loading, the hydrogen chemisorption on Co/Al 2 O 3 was significantly blocked leading to increased selectivity for heavier hydrocarbons during CO hydrogenation.…”

Effect of Vanadium Promotion on Activated Carbon-Supported Cobalt Catalysts in Fischer–Tropsch Synthesis

“…A number of studies have demonstrated that addition of modifiers (e.g. Pt [5], Ru [6,7], Re [8], La [9,10], Zr [11,12], Th [13]) to cobalt catalysts can increase reducibility, activity and selectivity to long chain hydrocarbon. It is mentioned in the literature that V-promoted Rh catalysts could significantly improve both the activity and selectivity towards the formation of C 2 oxygenates such as ethanol and acetic acid [14].…”