R. Dziembaj

Transformation of nitrogen structures in carbonization of model compounds determined by XPS

Abstract Nitrogen-containing chars were prepared by low-temperature carbonization (460 °C) of compounds containing pyrrolic, pyridinic, amino and cyano groups. The changes of precursor functionalities and transformation of nitrogen structures at 600 and 800 °C were determined by X-ray photoelectron spectroscopy. From all precursors, at low-temperature carbonization, three types of nitrogen structure were obtained: pyrrolic, pyridinic and quaternary, but from a precursor containing cyano groups this group was also observed. The concentration of pyrrolic and pyridinic structures decreases with increasing calcination temperature, whereas the amount of quaternary nitrogen increases. Quaternary nitrogen is the most stable form of the observed nitrogen structures, but an additional peak appeared at 403 eV for chars calcined at 800 °C.

Screening of catalysts in the oxidative dehydrogenation of ethylbenzene with carbon dioxide

The influence of the type and concentration of transition and alkali metal oxides, type of the catalyst support as well as pretreatment method on catalytic activity and stability of catalysts in the dehydrogenation of ethylbenzene in the presence of carbon dioxide was determined. Active carbon-supported iron oxide promoted by alkali metal oxide was found to show the highest performance in the reaction. An increase in the catalyst mass was observed during time-on-stream. Additionally the specific surface area of the catalyst decreased. Temperature programmed oxidation showed the presence of carbon deposits which could only be gasified above 700°C.

Nickel doped hydrotalcites as catalyst precursors for the partial oxidation of light paraffins

Abstract A series of Ni, Mg and Al containing hydrotalcite-type precursors was synthesised (Ni X Mg 72− X Al 28 , X =10–72) by coprecipitation at low supersaturation at pH 8±0.2 at 60–70°C. Their calcination at 900°C in air resulted in the formation of solids consisting of spinel and divalent metal oxide phases. The catalyst activation was studied by temperature programmed reduction (TPR). Ni 2+ in the divalent metal oxide phase could be reduced in all samples, with the reduction temperatures increasing with decreasing Ni content, but only in the sample without Mg the Ni 2+ in the spinel phase were reducible. The Ni dispersion determined from the TPR results was higher for the catalysts with a lower Ni content and decreased for higher Ni contents. Catalytic tests were carried out at 700°C and at 800°C for 240 min using a C 3 H 8 /O 2 /He-mixture at a gas hourly space velocity (GHSV) of 900 dm 3 g −1 h −1 . High values for the conversion of C 3 H 8 (≥73%) as well as for the selectivities to CO (≥88%) and H 2 (≥69%) were observed for all the catalysts at both reaction temperatures. At lower temperatures and with higher Ni content, these values were lower, whereas the conversion of O 2 was found to be almost complete in all experiments. The carbon content of the spent catalysts was determined by temperature programmed combustion (TPC) using thermogravimetry (TG). The tendency towards carbon formation was found to be higher at lower temperatures and for higher Ni contents. On the basis of activity, selectivity and resistance against coke formation, the Ni containing catalyst with the lowest Ni content was found to be the best catalyst.

Oxidative dehydrogenation of ethylbenzene with carbon dioxide on alkali‐promoted Fe/active carbon catalysts

The catalytic behavior of iron supported on activated carbon was investigated in the oxidative dehydrogenation of ethylbenzene. CO2 was applied as oxidant. High ethylbenzene conversion (>70%) and selectivity towards styrene (>90%) were observed at 550 °C. Apart from styrene, benzene, toluene, carbon monoxide and water were formed as products.

Characterization and activity of novel copper-containing catalysts for selective catalytic reduction of NO with NH3

Abstract Cu/Mg/Al mixed oxides (CuO = 4.0–12.5 wt%), obtained by calcination of hydrotalcite-type (HT) anionic clays, were investigated in the selective catalytic reduction (SCR) of NO by NH3, either in the absence or presence of oxygen, and their behaviours were compared with that of a CuO-supported catalyst (CuO = 10.0 wt%), prepared by incipient wetness impregnation of a Mg/Al mixed oxide also obtained by calcination of an HT precursor. XRD analysis, UV-visible-NIR diffuse reflectance spectra and temperature-programmed reduction analyses showed the formation, in the mixed oxide catalysts obtained from HT precursors, mainly of octahedrally coordinated Cu2+ ions, more strongly stabilized than Cu-containing species in the supported catalyst, although the latter showed a lower percentage of reduction. The presence of well dispersed Cu2+ ions improved the catalytic performances, although similar behaviours were observed for all catalysts in the absence of oxygen. On the contrary, when the mixture with excess oxygen was fed, very interesting catalytic performances were obtained for the catalyst richest in copper (CuO = 12.5 wt%). This catalyst exhibited a behaviour comparable to that of a commercial V2O5–WO3TiO2 catalyst, without any deactivation phenomena after four consecutive cycles and following 8 h of time-on-stream at 653 K. Decreasing the copper content or increasing the calcination time and temperature led to considerably poorer performances and catalytic behaviours similar to that of the CuO-supported catalyst, due to the side-reaction of NH3 combustion on the free Mg/Al mixed oxide surface.

Preparation and characterization of new Mg–Al–Fe oxide catalyst precursors for dehydrogenation of ethylbenzene in the presence of carbon dioxide

Abstract New catalysts based on hydrotalcite-like precursors (Mg–Fe and Mg–Al–Fe) were synthesized. The structure of catalyst precursors was confirmed by XRD, FT–IR and TG. Appearance of separate brucite phase was observed for Mg–Fe precursors with excess of Mg, while for Mg–Al–Fe precursors, increase in Al content led to a formation of MgAl 2 (OH) 8 and mixed Al–Fe hydroxides apart from hydrotalcite phase. During calcination, the hydrotalcite like precursors spread their surface area and transform into mixed oxide. The mixed oxides were applied in ethylbenzene (EB) dehydrogenation with CO 2 . The activity losses with time-on-stream were completely restored by oxygen pulses.

Pillared smectite modified with carbon and manganese as catalyst for SCR of NOx with NH3. Part II. Temperature‐programmed studies

Temperature‐programmed desorption (TPD) and surface reaction (TPSR), and additionally FTIR spectroscopy of adsorbed NO molecules were used to characterise surface sites on pillared smectites modified with carbon and manganese. Much higher adsorption of NH3 than NO was found, but acidic pre‐treatment increased NO sorption to comparable values as well as catalytic performance in SCR of NOx. In this case formation of strongly bound NO3− species was recognised, which reacted with NH3 at a temperature 200 °C higher than weaker adsorbed NO.

Synthesis, thermal and electrical properties of Li1+δMn2−δO4 prepared by a sol–gel method

Abstract The Li 1+ δ Mn 2− δ O 4 samples (0.00≤ δ ≤0.20) were obtained by a sol–gel method and characterized using: chemical analyses, XRD, SEM, TGA, DSC, electric conductivity and thermoelectric power. The obtained results were discussed in relation to the calcination temperature, and to the results obtained on commercial LiMn 2 O 4 . The samples calcined at 300 °C (S-samples) consisting small excess of Li ( δ ≤0.04) showed no phase transition at 285 K and no disturbance in electric conductivity and thermoelectric power, as observed for the related samples calcined at 800 °C (H-samples). Partial thermal decomposition of the S-samples or oxygen uptake by the H-samples were observed during TGA experiments above 350 °C. The beginning of the thermal decomposition of the H-samples started at higher temperatures, depending on Li-contents. At about 920 °C, the rapid acceleration took place independently on type of the samples. The thermal decomposition up to 800 °C seems to be reversible, owing to the samples reoxidation.

Catalytic conversion of ethyl alcohol on polyaniline protonated with 12-tungstosilicic acid

Abstract It has been demonstrated that protonation of polyemeraldine base with 12-tungstosilicic acid leads to the preparation of a new, polymer supported catalyst which shows significantly higher activity and altered selectivity in ethyl alcohol conversion as compared to crystalline 12-tungstosilicic acid studied in the same experimental conditions. The improved activity is associated with higher dispersion of Keggin units bonded to the polymer surface via protonation reaction which in turn leads to their improved thermal stability as shown by DTA, FTIR and other studies.

XPS study of polyaniline supported dodecatungstosilicic acid catalyst

Abstract The presence of hydrogenoheteropolyanions at the polyaniline surface supported H 4 SiW 12 O 40 catalyst playing most probably the role of catalytically active Bronsted acid centers in cumene cracking was confirmed by the XPS measurements. These centers are partially removed by heating at 573 K in the atmosphere of dry air but easily regenerated by the water vapor introduced into the reactor in the stream of helium carrier gas.