Effect Of Potassium Doping Research Articles

Alkali Resistant Fe-Zeolite Catalysts for SCR of NO with NH3 in Flue Gases

Fe-zeolite catalysts were prepared by ion-exchange and characterized by nitrogen physisorption, electron paramagnetic resonance (EPR) spectroscopy, NH3-temperature programmed desorption (TPD), H2-temperature programmed reduction (TPR) and Energy dispersive X-ray spectroscopy (EDX) methods. The effect of potassium doping on the acidic and redox properties of the Fe-zeolite catalysts were studied. The prepared catalysts showed high surface area and surface acidity. This is essential for increased alkali resistivity in comparison with conventional metal oxide supports like, e.g. TiO2 and ZrO2, towards e.g. potassium salts in flue gases from biomass fired power plants. These properties allowed both undoped and potassium doped Fe-zeolite catalysts to posses high activity during the selective catalytic reduction (SCR) of NO with NH3. The extent of deactivation of the Fe-zeolite catalysts was further compared with commercial V2O5–WO3–TiO2 catalyst (VWT) with various levels of potassium poisoning. While VWT catalysts severely deactivated at relative low potassium concentration levels the Fe-zeolite catalysts also showed superior alkali resistivity even at high potassium loadings.

Vanadia-based SCR catalysts supported on tungstated and sulfated zirconia: Influence of doping with potassium

A series of vanadium-based SCR catalysts supported on sulfated or tungstated ZrO2 were synthesized and characterized by means of N2-BET, XRD, NH3-TPD and in situ Raman spectroscopy. The effect of potassium doping on the properties of vanadia species was studied in detail. A number of catalyst preparation parameters were examined, including the choice of precipitant, variation of carrier surface area, potassium poisoning, crystallinity, and ZrO2-phase composition. The results show that the catalyst structure and SCR activity are affected from the synthesis route by the support crystallinity and morphology, the surface composition, and the molecular configuration of the dispersed vanadates. It was observed that poisoning with potassium had a negligible effect on the surface vanadate species (especially the VO stretching frequency observed by in situ Raman spectroscopy) if supported on the sulfated zirconia. Conversely, a more pronounced influence on the structure of surface vanadate was observed for the corresponding unsulfated samples, in which a significant red shift in the VO stretching frequency was observed on potassium doping. Computational studies suggested that potassium was responsible for both the observed decrease in VO stretching frequency and the higher proportion of dimers and higher polymers through coordination between K+ and two neighbouring VO. The results suggest an increased resistance toward potassium doping for the vanadia-based catalysts supported on sulfated zirconia.

Study of potassium additive on the phase formation and ferroelectric properties of 0.9PMN–0.1PT ceramics

A recent and innovative method to include Ti into the columbite precursor has permitted to synthesize 0.9PMN–0.1PT powders with high homogeneity. The present work describes this methodology, named modified columbite method, showing that the reaction between MN T and PbO at 800 °C for 2 h results in perovskite single-phase. The crystal structure alterations in the columbite and perovskite phases obtained by this methodology and the effects of potassium doping were investigated by the Rietveld method. Changes in the powder morphology, density and weight loss during the sintering process were also studied. Conclusively, potassium does not affect significantly the perovskite amount, but reduces the particle and grain sizes. This dopant also changes the relaxor behavior of 0.9PMN–0.1PT ceramic, reducing the dielectric loss and enhancing the diffuseness of the phase transition.

Modification of Electronic Properties of Mo2C Catalyst by Potassium Doping: Impact on the Reactivity in Hydrodenitrogenation Reaction of Indole

The effect of potassium doping on electronic surface properties of molybdenum carbide (Mo2C) was investigated by species-resolved thermal alkali desorption techniques, work-function measurements, a...

Effect of Potassium Doping on the Catalytic Behavior of Mo–V–Sb Mixed Oxide Catalysts in the Oxidation of Propane to Acrylic Acid

Small addition of potassium to a Mo–V–Sb mixed oxide catalyst (previously prepared by hydrothermal synthesis) strongly modifies its catalytic behavior. Thus, while acetic acid is mainly observed in the K-free catalysts, acrylic acid is selectively obtained in K-doped catalysts. In this case, a selectivity to acrylic acid of about 30% is achieved at propane conversions of 30%. This catalytic behavior is apparently not due to modification of the crystalline phases in the K-doped catalysts but to the elimination of the acid sites of the undoped Mo–V–Sb mixed oxide catalyst.

Electronic structure of potassium-doped carbon nanotubes

We present a density functional study of zigzag carbon nanotubes containing potassium atoms inside. We find that the effect of potassium doping is not simple charge transfer. The nearly free electron state of nanotube couples with the $\mathrm{K} 4s$ orbital. The state comes downward as the tube is thicker and crosses the Fermi level when the diameter is as large as $0.8--1\mathrm{nm}$. It is distributed near the center of the tube and extends to the tube direction, which suggests high conductivity via this state.

Effect of potassium doping on the structural and catalytic properties of V/Ti-oxide in selective toluene oxidation

Small addition of potassium to V/Ti-oxide catalyst (K:V=0.19), consisting of 3.7 monolayer VO x , increased activity and selectivity in partial oxidation of toluene. In order to elucidate the nature of vanadia species formed on the surface of V/Ti-oxide upon potassium doping, the catalysts were studied by transient kinetics method. The transient product responses during toluene oxidation by the oxygen present in the catalyst were compared for K-doped and non-doped samples. The formation of CO 2 decreased and formation of benzaldehyde increased with addition of potassium. This suggests a lower surface concentration of electrophilic oxygen (O −, O 2 −), which is usually responsible for the deep oxidation, and a higher concentration of nucleophilic oxygen (O 2−), responsible for the partial oxidation. The catalysts were characterised by means of HRTEM, FT-Raman spectroscopy and 51V NMR. Potassium addition introduces a disorder in the crystalline structure of bulk V 2O 5 particles resulting in better spreading of V 2O 5 over TiO 2 surface. The interaction of V 2O 5 with TiO 2 was facilitated upon K-doping, leading to the increased formation of monomeric vanadia species, which are the active sites in toluene partial oxidation to benzaldehyde.

The effect of potassium doping on the strength of molybdenum

It has been demonstrated that the mechanical strength of the Group VIB refractory metals exhibits a strong size dependence. It is also recognized that the recrystallization behavior of refractory metals can be influenced strongly by the presence of small amounts of impurities. A well-known example is tungsten and its alloys. Considerable evidence has been presented demonstrating the important role of oxides and potassium bubbles in increasing the recrystallization temperature and preventing grain growth in tungsten at high temperatures. Despite some controversy about the exact species that is responsible for the above effect, this experimental result has been used commercially to produce long-life lamp filaments. Amongst refractory metals, molybdenum exhibits some special thermal properties, including a low coefficient of thermal expansion and high thermal conductivity. These properties make molybdenum an attractive choice for high temperature applications where dimensional stability is of concern. The addition of a slight amount (approximately 0.002 - 0.02 wt%) of CaO and MgO considerably increases the primary recrystallization temperature of molybdenum. These results illustrate the effect of oxide impurities on molybdenum. Therefore, it is conceivable that potassium doping of molybdenum can also produce a similar effect, specifically, inhibition of grain growth, as it does to tungsten. Inmore » this study, the authors demonstrate this effect, and furthermore, discuss the effect of the presence of potassium on the strength of molybdenum.« less