Beata Stasińska

Effects of small MoO3 additions on the properties of nickel catalysts for the steam reforming of hydrocarbons

Bimetallic NiMo catalysts deposited on alumina show unusual properties when used in the steam reforming of hydrocarbons. An introduction of small amounts of molybdenum compounds (≤0.1 wt.-%) considerably reduces the detrimental effect of carbon deposit formation and increases the activity of methane steam reforming. With larger amounts, one observes a decrease in the catalyst activity, although it is much smaller than the reduction of the coling rate. The properties of the NiMoAl2O3 catalysts depend on the hydrogen-steam ratio in the reaction mixture which affect the mean degree of oxidation and distribution of various molybdenum states on the surface.

Complete Oxidation of Methane over Palladium Supported on Alumina Modified with Calcium, Lanthanum, and Cerium Ions

Abstract The activity and thermal stability of Pd/Al 2 O 3 and Pd/(Al 2 O 3 +MO x ) (M=Ca, La, Ce) palladium catalysts in the reaction of complete oxidation of methane are presented in this study. The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide. Then they were impregnated with palladium nitrate solution. The catalysts with unmodified alumina had a high surface area. The activity and thermal stability of the alumina- supported catalyst was also very high. The introduction of calcium, lanthanum, or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method. These modifiers decreased the activity of palladium catalysts, and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al 2 O 3 . The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.

Catalysts for the utilization of methane from the coal mine ventilation air

Catalysts for the utilization of methane from the coal mine ventilation air The paper indicates coal mines as the source of permanent emission of low-concentrated gases, which have increased the greenhouse effect. This paper proposes the catalytic oxidation of methane as the solution to the problem of methane utilization when its concentration in the air is insufficient for flame combustion. The studies which have been conducted for many years enabled finding the active oxide and metallic catalytic systems for the reaction of methane oxidation. For the utilization of gases with low-concentrated methane, using the low-temperature catalysts, especially palladium catalysts, seems to be economically well-justified. Depending on technological solutions it can be considered as the method for methane utilization or as an environmentally friendly way for the generation of electric and thermal energy.

Nickel-promoted Catalysts in the Reforming of n-Butane with CO2 or H2O

Studies of the reforming of n-butane by steam and carbon dioxide have been undertaken employing commercial catalysts such as Ni/α-Al2O3 modified by small additions of promoters such as K, Ba, Ce, W and Mo compounds. It was found that promoters improved the resistance of the catalyst towards coking, with this effect being smaller where CO2 was employed in the reforming reaction than when steam was used. The dynamics of the growth of the carbon deposit on the catalyst surface depended on the promoters employed as well as on the operating conditions; however, in the CO2 reforming of n-butane, such coking was more pronounced than in steam reforming. Use of the TPO method with oxygen or CO2 did not reveal considerable differences between the coke deposits formed during the reforming of n-butane with CO2 or H2O on the catalysts examined.

Carbon deposition studies in the steam reforming of methane using an equilibrated mixture

Nickel catalysts are commonly used in many industrial processes including the hydrogenation, hydrotreatment, hydrogenolysis, methanation and steam reforming of hydrocarbons. One of the important problems associated with these processes is the coking of such catalysts and in the present paper a new technique for measuring the coking rate in the steam reforming of hydrocarbons is presented. The methodology employed eliminates objections raised concerning gravimetric methods which are most frequently employed in the study of the rate of coking of catalysts. Qualitative agreement between the results obtained using both methods was demonstrated for catalysts differing both in composition and texture. The new method allows a better characterization of the resistance towards coking of nickel on various supports and in the presence of various promoters.

Influence of hydrogen on the properties of nickel-molybdenum catalysts in the steam reforming of hydrocarbons

It is well known that the presence of hydrogen influences the activity of a nickel catalyst in the steam reforming of hydrocarbons. The properties of nickel–molybdenum catalysts in such reactions depend on the kind of atmosphere employed since the effects of the partial pressure of hydrogen on the coking rate of nickel or of nickel–molybdenum catalysts are different. The changes observed depend on the presence and amount of promoter, although changes in the rate of coking for promoted catalysts at increased partial pressures of hydrogen in the reaction mixture cannot be explained solely in terms of changes in their activity. When all the experimental results and literature information are taken into account, it appears that the distribution of various MoOx surface sites plays an important role in the behaviour of nickel–molybdenum catalysts.