Cobalt doped catalysts

Further evidence for the catalytic importance of amorphous material comes from experiments carried out with cobalt-doped catalysts. Hutchings et al. (217) found that doping of the catalysts with cobalt improved their performance. Moreover, Sajip et al. (148) found that the cobalt-promoted catalysts are far more disordered than the undoped catalysts. In the doped catalysts, the promoter is dispersed in the amorphous phase, and cobalt is not found in the vanadyl pyrophosphate crystals. It is thought that one of the properties of the cobalt promoter is to stabilize the disordered phase and V -containing phases in the final catalysts, which leads to improved performance. This suggestion implies that the disordered material is the catalytically active vanadium phosphate phase. 

This phenomenon has also been observed for catalysts prepared using an aqueous route (182). Both the iron and cobalt promoters led to an increase in selectivity. The iron-promoted catalyst was characterized by an increase in activity, but the cobalt-promoted catalyst was characterized by a decrease in activity. The decrease in activity of the cobalt-doped catalyst was attributed to the formation of VOPO4 in the final catalyst. The VOPO4 is formed by the oxidation of V0HP04 1 H20 during the introduction of the promoters in the incipient wetness technique. A similar effect was reported for catalysts doped with indium and tetraethy-lorthosilicate (TEOS) (181). The improved performance was observed only with both promoters in the catalyst. It was proposed that the... 

Discussion. These results show clearly that although copper crystallites are present in the reduced, cobalt-doped catalysts, the copper surface is not available for catalysis or chemisorption. 

Hutchings (170) plotted (Figure 31) the activity against the surface area for a number of promoted catalysts and deduced that most of the catalysts conform to a linear correlation. The only enhancement of the specific activity was observed for the cerium-promoted catalyst. This result shows that care must be taken in the interpretation of the catalyst performance data, particularly when catalysts prepared by different methods are compared. In a separate study, Hutchings and Higgins (171) found that chromium, niobium, palladium, antimony, ruthenium, thorium, zinc, and zirconium each had very little effect on the specific activity of (VO)2P207. A significant increase in surface area was observed with zirconium, zinc, and chromium, which could be of use as structural promoters. Iron-, cesium-, and silver-doped catalysts decreased the specific activity, and cobalt and molybdenum were the only promoters found to increase the specific activity. 

Zazhigalov et al. (209) investigated cobalt-doped vanadium phosphate catalysts prepared by coprecipitation and impregnation methods. The performance of catalysts prepared by both methods was improved as a consequence of the promotion. The cobalt is thought to have been present as cobalt phosphate, which is considered to stabilize excess phosphorus at the surface, which has previously been foimd to be an important characteristic of active catalysts. 

Metal-Doped Catalyst Systems and the Structure of Cobalt(II,III)... 

Equilibrium and Kinetic Aspects of Strong Metal-Support Interactions in Pt-Ti02 and Cobalt-Doped Cu-Zn0-AI203 Catalysts... 

A set of three Co-doped precursors (with 1, 2 and 5 wt% Co) were prepared by dissolving the required amount of cobalt acetylacetonate in isobutanol prior to the operation of refluxing with isobutanol and 85% H3PO4. The subsequent filtration, washing and doping procedures were identical to that employed for the undoped precursor. These doped catalysts were then activated for 25h at 400°C under the same reaction mixture and flow conditions as described previously. 

The catalytic performance of the Co-doped catalysts was compared to that of an undoped VPO catalyst activated for the same time period. The results of our analysis are presented in Table 2, where it is clear that the addition of Co in all cases has a beneficial effect on both the selectivity to maleic anhydride production and the specific activity of the VPO catalyst. The most significant improvement, however, was noted for the catalyst with the lowest cobalt loading. 

The effects of doping the Li/MgO catalyst with 2 mol % transition metal relative to lithium (100 M(M + Li) mol basis) is shown in Fig. 4. The presence of the transition metal generally, with chromium being the exception, increased the CHi, conversion at 800°C. In terms of C2 selectivity manganese, iron and cobalt were most effective. A temperature dependent study shewed that the Mn doped catalyst had comparable activity to an undoped Li/MgO catalyst at 50°C lower tanperature. The effect of CO on activity of Mi/LiMgO catalyst was also determined. As the partial pressure of CO in the reactant mixture was increased the conversion of methane decreased and the selectivity to C2 increased (Fig. 5). 

Activity. A comparison of the global rates of CO conversion on a per gram of catalyst or on a per gram of cobalt in the catalyst at 500 K shows that the activities of the chromium- and zirconium-doped catalysts were substantially higher than any of the other catalysts studied. (Specific rates on a per active catalyst site basis (13,21) are not available for these catalysts. Such measurements will be undertaken for the more promising catalysts in the near future (22). Justification for this use of the continuous stirred-tank reactor (CSTR) design equation was provided by pulse tracer experiments (20).) These are followed by the activated carbon-... 

A series of cobalt-doped vanadium phosphorus oxide catalysts was prepared using a classical organic method, followed by calcination, and tested for the oxidation ofbenzyl alcohol with TBHP as an oxidant.The catalytic activity increases with the temperature growth up to 68% at 90 °C, while selectivity toward benzaldehyde varies in different solvents and reaches... 

Scheme 54 Oxidation of benzyl alcohol with cobalt-doped vanadium phosphorus oxide catalysts ...

Mahdavi V, Hasheminasab HR. Vanadium phosphorus oxide catalyst promoted by cobalt doping for truld oxidation of benzyl alcohol to benzaldehyde in the liquid phase. 

There have been very few experimental studies examining membrane reactors for ATR, and all of them have dealt with Pd-based membranes. Recent collaborations, between the Films and Inorganic Membrane Laboratory at The University of Queensland in Australia and Saudi Aramco s Research and Development Center, on the use of sihca-based membrane reactors for the ATR of liquid fuels has yielded some promising experimental results. Cobalt-doped silica membranes (Uhhnann et ah, 2009) were incorporated with a commercial catalyst in an ATR catalytic membrane reactor to process a gasoline feed. In comparison to the fixed bed reactor (employing the same... 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

Figure 9.19 In situ Mossbauer emission spectra of 57Co in (left) a series of sulfided Co-Mo/A1203 catalysts and (right) MoS2 particles doped with different amounts of cobalt, corresponding to Co/Mo ratios of a) about 3 parts per million, b) 0.05 and c) 0.25. The Co-Mo-S phase, active in the HDS reaction, has a spectrum unlike that of any bulk cobalt sulfide and is most clearly observed in the spectra of Co-Mo/Al203 catalysts of low Co content, and in the MoS2 particles doped with ppms of cobalt (from Wivel et al. [70] and Topspe et al. [71]).

Mossbauer Measurements. Co-Mo catalysts cannot be studied directly in absorption experiments since neither cobalt nor molybdenum has suitable Mossbauer isotopes. However, by doping with 57Co the catalysts can be studied by carrying out Mossbauer emission spectroscopy (MES) experiments. In this case information about the cobalt atoms is obtained by studying the 57Fe atoms produced by the decay of 57Co. The possibilities and limitations on the use of the MES technique for the study of Co-Mo catalysts have recently been discussed (8., 25.). 

Fig. 9.19 In-situ Mossbauer emission spectra of 57Co in a series of sulfided C0-M0/AI2O3 catalysts (left) and M0S2 particles doped with different amounts of cobalt (right), corresponding to Co/Mo ratios of (a) about 3 ...

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