Nickel catalyst temperature-programmed

J.G. McCarty, P.Y. Hou, D. Sheridan, and H. Wise, Reactivity of Surface Carbon on Nickel Catalysts Temperature-Programmed Surface Reaction with Hydrogen and Water, in Coke Formation on Metal Surfaces, eds. L.G. Albright and R.T.K. Baker, American Chemical Society, Washington D.C., 1982, p. 253. 

Reactivity of Surface Carbon on Nickel Catalysts Temperature-Programmed Surface Reaction with Hydrogen and Water... 

JG McCarty, PV Hou, D Sheridan, H Wise. Reactivity of surface carbon on nickel catalysts temperature-programmed surface reaction with hydrogen and water. In LF Albright, RT Baker, eds. Coke formation on metal surfaces. Washington, DC American Chemical Society, 1982. 

Brown, R., Cooper, M., and Whan, D. 1982. Temperature programmed reduction of alumina-supported iron, cobalt and nickel bimetallic catalysts. Appl. Catal. 3 177-86. 

Figure 2. Temperature Programmed Reduction of Ni contaminated catalyst components a) non-zeolitic particles with 10,100 ppm Ni b) zeolitic particles with 10,860 ppm Ni. These materials were impregnated using nickel naphthenate and then steamed (1450°F, 4 hrs, 90% steam, 10% air) prior to running the TPR. The Ni on the non-zeolitic particles reduced at a lower temperature than that on the zeolitic particles.

Hydrosilicate formation is also in evidence in the Cu(II)-Si02 system. Via precipitation from a homogeneous solution one can obtain highly dispersed copper oxide on silica (cf. above, Fig. 9.10, where it should be noted that the Cu case is more complicated than the Mn one in that intermediate precipitation of basic salts can occur). Reaction to copper hydrosilicate is evident from temperature-programmed reduction. As shown in Fig. 9.12 the freshly dried catalyst exhibits reduction in two peaks, one due to Cu(II) (hydr)oxide and the other, at higher temperature, to Cu(II) hydrosilicate. Reoxidation of the metallic copper particles leads to Cu(II) oxide, and subsequent reduction proceeds therefore in one step. The water resulting from the reduction of the oxide does not produce significant amounts of copper hydrosilicate, in contrast to what usually happens in the case of nickel. 

The molybdenum dispersion also depends on the phosphorus content of the catalyst. Atanasova et al. (68, 87) reported that the dispersion of molybdenum and nickel, measured by X-ray photoelectron spectroscopy (XPS), shows a steep increase due to the presence of phosphorus at low loadings. The dispersion of molybdenum in NiMoP/Al catalysts increases further as a result of calcination, whereas that of nickel decreases. In contrast, Sajkowski et al. (83) reported, on the basis of an extended X-ray absorption fine structure (EXAFS) investigation, that phosphorus does not affect the size of the polymolybdate species, Mangnus et al. (31) inferred that the stacking of molybdates does not increase as a result of the addition of phosphorus since the height of a temperature-programmed reduction (TPR) peak at 400°C due to the reduction of deposited multilayered molybdenum oxo-species was found to be independent of the phosphorus content. However, Chadwick el al. (60) concluded from XPS measurements that the dispersion of molybdenum decreases upon addition of phosphorus. 

Sulfur desorption fiom the poisoned nickel catalysts was studied by temperature programmed hydrogenation (TPH). The poisoned catalyst beds were powdered to homogenize them. Approximately 0.5 g of powdered catalyst was placed in an atmospheric quartz tube reactor which had a thermocouple shield. The reaction gas was argon/hydrogen (70% Ar/30% Hj). The content of hydrogen in the gas was about the same as in the sulfurpoisoning tests. 

Figure 2. Temperature-programmed hydrogenation of sulfur from poisoned nickel catalysts (Al, A2 and C). Heating rate 20°C/min, gas atmosphere Ar/Hj.

The nature of the carbon deposits formed on an alumina-supported nickel catalyst have been characterized by their reactivity with H2 and H 0 during temperature-programmed surface reaction (TPSR). 

Fig. 1 Temperature-programmed desorption spectra of unpromoted and promoted nickel-alumina catalysts.

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