Tadeusz Borowiecki

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.

Carbon deposition on Ni/Al2O3 catalysts doped with small amounts of molybdenum

High resolution transmission electron microscopy (HRTEM) was used in the study of the structure of carbon deposits obtained on Ni/Al2O3 and Ni–Mo/Al2O3 catalysts during steam reforming of n-butane. The introduction of small amounts of molybdenum compounds (≤ 1 wt% of Mo) into the nickel catalysts greatly improved their resistance to coking. The morphology of carbon is similar on both catalysts. On the Ni–Mo/Al2O3 catalyst much lower numbers of Ni particles were observed that are active in the carbon filaments growth.

Influence of molybdenum and tungsten additives on the properties of nickel steam reforming catalysts

An introduction of small amounts of molybdenum and tungsten compounds into the nickel catalyst of the steam reforming of methane considerably reduces the detrimental effect of carbon deposit formation, while entailing no change in the catalyst activity.

A new preparation technique of catalysts characterized by small metal crystallites

The present study reports a new and original technique for obtaining nickel catalysts characterized by small metal crystallites. The catalysts were prepared on γ-Al2O3. The total surface of the carrier was 37.5 m2/g. The preservation of the appropriate procedure and conditions of preparation allow a large expansion of active nickel surface (mean crystallite size 2.0–3.0 nm) in spite of the quite hard conditions of reduction (773 K and 3 h).AbstractВ данном сообщении приводится новая и оригинальная техника получения никелевых катализаторов, характеризуемых малыми металлическими кристаллитами. Катализаторы были приготовлены на γ-Al2O3. Общая поверхность носителя равнялась 37,5 м2/г. Соблюдение подходящей процедуры и условий приготовления приводит к большому повышению активной поверхности (средние размеры кристаллита 2,0–3,0 нм) несмотря на относительно жесткие условия восстановления (3 часа при 773 К).

On the applicability of Arrhenius plot methods to determine surface energetic heterogeneity of adsorbents and catalysts surfaces from experimental TPD spectra.

Recovering adsorption energy distribution from experimental data belongs to most difficult problems of adsorption science. In the case when thermodesorption data are used as a source of information, that difficult problem is overcome by the common use of the Arrhenius plot methods. So, we decided to carry out an extensive model investigation to show, how reliable information concerning the surface energetic heterogeneity is obtained by using the Arrhenius plot methods. Like in our previous publications we have used the Statistical Rate Theory of Interfacial Transport to describe the adsorption/desorption kinetics. Our model investigations showed, that the Arrhenius plot methods, cannot provide reliable information about the surface energetic heterogeneity. Moreover, for strongly heterogeneous surfaces a linear relationship exists between the logarithm of the pre-exponential constant and the adsorption energy, for certain adsorption coverages. That kind of compensation effect has, so far, been ascribed to interactions between the adsorbed molecules. The failure of the popular Arrhenius plot method puts, as an urgent agenda, the development of reliable methods for recovering adsorption energy distribution from the thermodesorption data.

The influence of promoters on the coking rate of nickel catalysts in the steam reforming of hydrocarbons

The effect of small amount of different promoters (K, Ba, Mo, W and Ce) on the properties of the nickel catalysts in steam reforming were investigated. The experimental results show that only the cerium promoter has very favourable influence on the nickel dispersion and its resistance for sintering. On the contrary the cerium promoter does not have the influence on the decrease of the rate of carbon formation in the steam reforming of n-butane.

Thermodesorption studies of energetic properties of nickel and nickel-molybdenum catalysts based on the statistical rate theory of interfacial transport

The new theoretical approach to adsorption/desorption kinetics, called the statistical rate theory of interfacial transport, is used to analyze quantitatively spectra of hydrogen thermodesorption from alumina-supported nickel and nickel-molybdenum catalysts. A new more accurate method is developed to calculate the distribution of the chemisorption energies on the surfaces of these two catalysts. The comparison of their adsorption energy distributions shows that the addition of molybdenum, changes relative mutual proportions of the four kinds of chemisorption sites existing on these catalysts surfaces. Changing these proportions is related to changing tendencies to coking formation and changing activities for methane steam reforming.

Promotion of methane conversion catalysts into higher hydrocarbons

Abstract The effects of the type of initial salt of a sodium promoter on the activity and selectivity of silica-supported manganese and lead catalysts, used in the oxidative coupling of methane, were investigated. The type of sodium salt is much less significant for catalysts containing an active phase which does not react with the support, e.g. MnO x /SiO 2 than for lead catalysts, where the presence of sodium facilitates phase transformations connected with the reactions of the support with the lead phase. The type and amount of the new phases are dependent on the sodium salt applied. For the former catalysts an increase in the activity and selectivity to hydrocarbons C 2+ was not accompanied by changes in the ratios of the compounds formed, e.g. C = 2 /C − 2 and C 3+ / C 2+ . The ratios of the lead catalysts are dependent on the kind of anion with which the sodium was introduced into the catalyst. With rising reaction temperatures the type of sodium salt used has a smaller significance.

Resistance to Coking Determination by Temperature Programmed Reaction of n-Butane with Steam

Resistance to coking is one of the most important characteristics of nickel catalysts used for steam reforming of hydrocarbons, CO2 reforming or methanation of carbon oxides. Microbalance reactors have for a long time played an important role in catalyst deactivation studies, providing coking and coke gasification rates. However, conventional thermogravimetric microbalances have a number of limitations. The aim of this paper is to compare initial temperatures of coking of Ni and Ni-Mo catalysts (with different resistance to coking) obtained in the temperature-programmed reaction of n-butane with steam with the results of coking rates obtained by the traditional thermogravimetric method. The investigations showed great agreement of the results.

Determination of resistance to coking in the steam reforming of hydrocarbons

For a long time the microbalance reactor has played an important role in catalyst deactivation studies, but it has a number of limitations. The initial temperatures of coking of Ni and Ni-Mo catalysts in the temperature-programmed reaction (TPReaction) of n-butane with steam are compared with the results of coking rates obtained by the traditional thermogravimetric method. The investigations show good agreement of the results.