Amount Of Adsorbed NO Research Articles

NOx-assisted soot oxidation based on Ag/MnOx-CeO2 mixed oxides

In previous studies, Ag/CeO2 catalyst showed the high activity on NOx-free soot oxidation. For additional improvement of oxidation activity, Mn was introduced in Ag/CeO2 and NOx-assisted soot oxidation was performed. NOx-assisted soot oxidation activities showed the large difference between the catalysts. Especially, Ag/2MnOx-1CeO2 catalysts showed remarkably improved T20 at 349 °C compared with T20 of Ag/CeO2 at 464 °C (each T50 is 391 °C and 400 °C, and each Tmax is 514 °C and 509 °C). NO oxidation activity was increased as the mole ratio of Mn increased, while amount of NO adsorption was increased in Ag/MnOx-CeO2 mixed oxide compared to other catalysts. Especially, Ag/2MnOx-1CeO2 catalysts showed NO oxidation activity at low-temperature and NO desorption at appropriate temperature. As a result, it was confirmed that not only the NO oxidation activity but also the NOx adsorption characteristics are the most important factors in NOx-assisted soot oxidation. Accordingly, Ag/2MnOx-1CeO2 catalysts were proposed as optimal catalysts.

PREPARATION OF HIGHLY ACTIVE Co-Mo/Al<sub>2</sub>O<sub>3</sub> HDS CATALYSTS WITH CITRIC ACID ADDITION BY THE POST-TREATMENT METHOD

A study of the influence of citric acid (CA) addition by a post-treatment method during the preparation of a series of Mo/Al2O3 catalysts on the thiophene HDS activity was conducted. The Mo/Al2O3 catalysts were also prepared by a chemical vapor deposition (CVD) technique using Co(CO)3NO to introduce Co atom and characterized by means of NO adsorption, XRD, Mo K-edge EXAFS and XRF. With 8.7 wt% Mo, citric acid was not affected very much for the Co-Mo/Al2O3 catalysts. On the other hand, an outstanding result was shown that the HDS activity was drastically enhanced by 5 times up to Mo content around of 25 wt% Mo. It is suggested that the post treatment increased the dispersion of MoS2 particles, in particular at a high Mo loading. This was also supported by the amount of NO adsorption and amount of Co anchored by the CVD results, which enhanced as the increasing Mo loading up to 25 wt% Mo. Moreover, Mo-CA complex species were observed on the post-treatment method and CVD technique was one of advanced method to prepare Co-Mo-S phases selectively.

THE EFFECTS OF BORON ADDITION AND PRESULFIDATION TEMPERATURE ON THE HDS ACTIVITY OF A Co-MoS<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> CATALYST

The effect of boron addition was studied on the hydrodesulfurization (HDS) of thiophene over Co-MoS2/B/Al2O3 (CVD-Co/MoS2/B/Al2O3), which was prepared by a CVD technique using Co(CO)3NO as a precursor of Co. The catalyst was characterized by means of NO adsorption, XPS, Raman Spectroscopy, FTIR, and TEM. The HDS activity of CVD-Co/MoS2/B/Al2O3 catalyst increased as the boron content increased up to about 0.6 and 1.2 wt% B for the catalyst presulfided at 673 and 773 K respectively, followed by a decrease with a further addition of boron loading. In spite of the activity increase, the amount of NO adsorption on MoS2/B/Al2O3 steadily decreased with increasing boron loading, suggesting that the dispersion of MoS2 particles is decreased by the addition of boron. Selective formation of the CoMoS phase on CVD-Co/MoS2/B/Al2O3 was achieved by the CVD technique. The TOF of the HDS over the CVD-Co/MoS2/B/Al2O3 catalyst, defined by the activity per Co atom forming the CoMoS phase, increased as high as 1.6 and 1.9 times for the catalyst presulfided at 673 and 773 K, respectively. It is concluded that the addition of boron weakens the interaction between Mo oxides and Al2O3 surface, promoting the formation of the so called Co-Mo-S ";;;pseudo";;; type II over CVD-Co/MoS2/B/Al2O3 presulfided at 673 K. The Co-Mo-S ";;;pseudo";;; type II is a metastable phase with the TOF value intermediate between Co-Mo-S type I and type II. With CVD-Co/MoS2/B/Al2O3 presulfided at 773 K, the addition of boron promotes the formation of ";;;real";;; Co-Mo-S type II, possibly by the formation of well-crystallized MoS2 structure. Keywords: Hydrodesulfurization; Co-Mo sulfide catalysts; Effect of boron addition; CVD technique; Turnover frequency

Effect of phosphorus addition on the active sites of a Co-Mo/Al2O3 catalyst for the hydrodesulfurization of thiophene

Abstract The effect of phosphorus addition was studied on the hydrodesulfurization (HDS) of thiophene over Co-MoS2/P/Al2O3, which was prepared by a chemical vapor deposition (CVD) technique using Co(CO)3NO as a precursor of Co. The catalysts were characterized by means of NO adsorption, FTIR and Raman spectroscopy. The HDS activity of Co-MoS2/Al2O3 was slightly increased by the addition of 0.2 wt% P, followed by a slight decrease with a further addition of phosphorus. In spite of the activity increase, the amount of NO adsorption on MoS2/P/Al2O3 steadily decreased with increasing phosphorus loading, suggesting that the dispersion of MoS2 particles is decreased by the addition of phosphorus. The TOF of the HDS over CVD-Co/MoS2/P/Al2O3 catalysts, defined by the activity per Co atom forming the Co-Mo-S phase, increased as much as 1.3 times by the addition of phosphorus, indicating that the active phase of the catalysts shifts from less active Co-Mo-S Type I to more active Co-Mo-S (pseudo) Type II. FTIR results showed that phosphoric acid reacts with the surface OH groups of Al2O3, resulting in weakened interactions between molybdenum oxides and Al2O3 surface and thus in less abundant Mo–O–Al bonds in MoS2–Al2O3 interactions.

Edge dispersion of supported MoS 2 and WS 2 catalysts as evaluated by using Co(CO) 3NO as a probe molecule

SiO 2- and Al 2O 3-supported MoS 2 and WS 2 catalysts were prepared to exploit the evaluation technique of the edge dispersion of MoS 2 and WS 2 particles. A chemical vapor deposition (CVD) technique using Co(CO) 3NO as a probe molecule was used for the evaluation. Results were compared with those from conventional techniques such as NO adsorption and TEM. A proportional correlation was obtained between the amount of NO adsorption and the amount of Co atoms accommodated by the CVD technique on WS 2/SiO 2 and WS 2/Al 2O 3 catalysts, demonstrating a selective location of the Co atoms on the edges of WS 2 particles, as previously established for MoS 2 catalysts. A comparison of the amounts of NO adsorption and Co accommodation on MoS 2 and WS 2 catalysts suggested a 70% higher density of sulfur vacancy on MoS 2 particles than on WS 2 particles regardless of the support. The Co atoms on the edges of MoS 2 and WS 2 particles showed the identical NO adsorption property. We propose that Co(CO) 3NO can be used as a probe molecule to evaluate and directly compare the edge dispersions of MoS 2 and WS 2 catalysts. The dispersion of MoS 2 particles was about two times higher than that of WS 2 particles with the SiO 2-supported catalysts. With the Al 2O 3-supported catalysts, MoS 2 and WS 2 particles were dispersed to a similar extent but much more highly dispersed than the counterparts in the SiO 2-supported catalysts. The evaluation of the edge dispersion of MoS 2 and WS 2 particles by means of TEM may pose problems when SiO 2- and Al 2O 3-supported catalysts are compared. The edges of unpromoted MoS 2 particles exhibited a significantly higher intrinsic activity for the HDS of thiophene than those of WS 2 particles.

Direct Decomposition of NO over Supported-alkaline Earth Metal Oxide Catalysts

NO decomposition over supported alkaline earth metal oxide catalysts was strongly dependent on the type of metal oxide support. Y 2 O 3 was the most effective support. Ba/Y 2 O 3 showed the highest NO decomposition activity, which decreased in the order of Ba/Y 2 O 3 > Sr/Y 2 O 3 > Ca/Y 2 O 3 > Mg/Y 2 O 3 ∼Y 2 O 3 . The catalytic activity of Ba/Y 2 O 3 for NO decomposition at 900°C gradually increased with reaction time. The activity enhancement was due to the decomposition of barium carbonate into barium oxide during the reaction. Barium carbonate was completely decomposed by reduction with H 2 at 900°C, resulting in significant enhancement of NO decomposition activity. The activity of Ba/Y 2 O 3 increased with higher barium loading up to 5 wt%, and then became constant. There was a strong relationship between NO conversion and the amount of NO adsorption on Ba/Y 2 O 3 , suggesting that NO adsorption sites are the reaction sites for NO decomposition. The relationship between the activity for 1-butene isomerization, which is an indicator for the basicity of Ba/Y 2 O 3 catalysts, and the activity for NO decomposition suggests direct participation of basic sites in the NO decomposition reaction over supported alkaline earth metal oxide catalysts.

The effect of boron addition on the hydrodesulfurization activity of MoS 2/Al 2O 3 and Co–MoS 2/Al 2O 3 catalysts

The effect of boron addition was studied on the hydrodesulfurization (HDS) of thiophene over MoS 2/B/Al 2O 3 and Co–MoS 2/B/Al 2O 3 (CVD-Co/MoS 2/B/Al 2O 3), which was prepared by a CVD technique using Co(CO) 3NO as a precursor of Co. The catalysts were characterized by means of NO adsorption and TEM. The HDS activity of MoS 2/B/Al 2O 3 catalysts kept constant up to a boron content of about 0.6 wt% and decreased with a further increase of boron content. With CVD-Co/MoS 2/B/Al 2O 3 catalysts, the HDS activity significantly increased as the boron content increased up to about 0.6 wt% of boron, followed by a decrease with a further increase of boron loading. Despite the activity increase, the amount of NO adsorption on MoS 2/B/Al 2O 3 steadily decreased with increasing boron loading, suggesting that the dispersion of MoS 2 particles is decreased by the addition of boron. A selective formation of the CoMoS phase on CVD-Co/MoS 2/B/Al 2O 3 was achieved by the CVD technique. The TOF of the HDS over the CVD-Co/MoS 2/B/Al 2O 3 catalysts, defined by the activity per Co atom forming the CoMoS phase, increased as high as 1.6 times by the addition of boron, indicating that the active phase of the catalysts shifts from less active CoMoS Type I to more active CoMoS Type II. A TEM analysis showed that the number of stacking of MoS 2 slabs was only slightly increased by the addition of boron. It is concluded that the activity increase of the CVD-Co/MoS 2/B/Al 2O 3 catalyst is caused by the formation of CoMoS Type II because of weakened interaction strength between the CoMoS phase and the Al 2O 3 surface by the addition of boron.

Photocatalytic oxidation of nitrogen oxide over titania–zeolite composite catalyst to remove nitrogen oxides in the atmosphere

The photooxidation of NO with oxygen over Hycom TiO2 and zeolite (A and Y form zeolite: TiO2-AZ and TiO2-YZ) composite catalysts was studied to remove NOx in the atmosphere. The photocatalytic oxidation activity of the titania in the composite catalyst in a proportion of AZ:TiO2=3:7 is about three times larger than that in the bare titania. The adsorption behaviors of NO and NO2 for the bare titania sample obey Langmuir adsorption equations of NO and NO2, respectively. In the titania–zeolite composite catalysts, the adsorption data indicate the increase in the amount of NO adsorption on the TiO2 phase and the decrease in the amount of NO2 adsorption, compared with the bare titania. The acceleration of NO photooxidation rate, resulting from the increase in the amount of NO adsorbed and the decrease in the amount of NO2 adsorbed, thus occurs on the TiO2 phase. IR spectra, when irradiating the catalysts with UV, showed the immediate formation of nitrate and NO2 species on the catalyst. The results lead to the conclusion that the zeolites promote the photocatalytic oxidation of NO over the titania.

Enhancement of NO adsorption on pitch-based activated carbon fibers by dispersion of CU-doped α-FeOOH fine particles

The effects of dispersion of ultrafine Cu-doped α-FeOOH particles on the surface of pitchbased activated carbon fibers (ACF) on their NO adsorption capacity were examined at 303 K. Nitrogen adsorption isotherms of the samples were determined at 77 K, and their microporosity characteristic data were obtained from α s and Dubinin-Radushkevich plots. The dispersion of α-FeOOH increased the saturation uptake of NO by pre-oxidized ACF (ox-ACF) by more than 50%. Cu doping of the dispersed α-FeOOH particles enhanced the NO adsorptivity of ox-ACF remarkably. The α-FeOOH-dispersed ox-ACF, heat treated at 773 K in vacuo, showed the largest amount of NO adsorption. However, no enhancement effects were observed in the case of ACF without preoxidation.

Effect of Water Vapor on the Selective Reduction of NO by Methane over Cobalt-Exchanged ZSM-5

The effect of water vapor on the reduction of NO with CH4 in excess O2 over a Co-ZSM-5 catalyst was studied. The presence of 2% water significantly decreases the NO conversion at T ≤ 450°C but has less of an effect at T ≥ 500°C. The selectivity of methane toward NO reduction was enhanced by the presence of water at low temperatures and is unchanged at high temperatures. This inhibition is reversible upon eliminating water from the system. The effect of water is dependent on the level of water added, space velocity, reaction temperature, and level of methane in the feed. The addition of water increases the empirical reaction order with respect to either CH4 or NO from a fractional order to first order. Temperature-programmed desorption studies show that the amount of NO adsorption on Co-ZSM-5 is significantly reduced if it is not fully dried, and the competitive adsorption between H2O and NO is probably the cause of the inhibition by water. In addition, Co-ZSM-5 is capable of removing NO and CO simultaneously in either a dry or wet feed.

Reaction of dimerized NOx (x = 1 or 2) with sulfur dioxide in a restricted slit-shaped micropore space

The reaction of dimerized NO or NO[sub 2] with SO[sub 2] in a slit-shaped micropore of [alpha]-FeOOH dispersed activated carbon fiber (ACF) at 273-373 K was examined using IR spectroscopy, [alpha]-FeOOH particles on ACF were ultrafine and strongly interacted with the carbon surface as examined by EXAFS and XPS. The micropore width of the ACF was 0.9 nm irrespective of dispersion of [alpha]-FeOOH by high-resolution N[sub 2] adsorption measurements. Significant amounts of NO molecules can be adsorbed in the micropore in the form of a dimer and react with adsorbed SO[sub 2] molecules in the micropore to produce N[sub 2]O. The effects of reaction temperature, gas composition of NO and SO[sub 2], and dispersion of [alpha]-FeOOH on the N[sub 2]O formation were examined; the reaction was governed by the amount of NO adsorption in the micropore. The N[sub 2]O formation arose from the disproportionation reaction of the dimerized NO to N[sub 2]O and NO[sub 2], where coexisting SO[sub 2] in the micropore was confirmed by diffuse reflectance FTIR measurement. In the case of the reaction of the dimerized NO[sub 2] with SO[sub 2] in the micropore, also N[sub 2]O and SO[sub 3] were produced via intermediate (NO)[sub 2]. Thus, themore » slit-shaped micropore can induce the high-pressure reaction of the disproportionation reaction of (NO[sub 2]) even under moderate conditions.« less

Effect of temperature on micropore filling of supercritical NO on Fe 2O 3-dispersed activated carbon fibers

The temperature dependence of NO adsorption on Fe 2O 3-dispersed activated carbon fibers was examined from 274 to 373 K. The percentage of the micropore volume occupied by NO relative to the micropore volume, determined from N 2 adsorption, decreased from 83 to 45% with increasing temperature. The changes in the initial rate of NO adsorption and in the saturated amount of NO adsorption with temperature suggested the assistance of chemisorptive process in the micropore filling of supercritical NO.