NO adsorption and temperature programmed desorption on K_2CO_3 modified activated carbons

Fuel cell stacks as the automotive power source can be severely poisoned by a trace amount of NOx in atmosphere,which makes it necessary to provide clean air for fuel cell vehicles.In this work,activating commercial activated carbons with K2CO3 for the large enhancement of NO capture was studied.K2CO3 modified activated carbons(K2CO3 ACs)were prepared by impregnating activate carbons in K2CO3 solution under ultrasound treatment,followed by temperature programmed baking at 800 oC.The dynamic NO flow tests on K2CO3 ACs at room temperature indicated that NO adsorption capacity reached the maximum(96 mg/g)when K2CO3 loading was 19.5 wt%,which corresponded to a specific surface area of 1196.1 m2/g and total pore volume of 0.70 cm3/g.The ten-fold enhancement of NO adsorption on K2CO3 ACs compared to the unimpregnated activated carbon was mainly attributed to the formation of potassium nitrite,which was confirmed by FTIR and temperature programmed desorption measurements.Regeneration tests of NO adsorption on the optimum sample revealed that 76%of the NO adsorption capacity could be remained after the fourth cycle.

Surface Chemistry of Ga（CH3）3 on Pd（111） and Effect of Pre-covered H and O

The adsorption and decomposition of trimethylgallium （Ga（CH3）3, TMG） on Pd（111） and the effect of pre-covered H and O were studied by temperature programmed desorption spectroscopy and X-ray photoelectron spectroscopy. TMG adsorbs dissociatively at 140 K and the surface is covered by a mixture of Ga（CH3）x （x=1, 2 or 3） and CHx（a） （x=1, 2 or 3） species. During the heating process, the decomposition of Ga（CH3）3 on clean Pd（111） follows a progressive Ga-C bond cleavage process with CH4 and H2 as the desorption products. The desorption of Ga-containing molecules （probably GaCH3） is also identi ed in the temperature range of 275-325 K. At higher annealing temperature, carbon deposits and metallic Ga are left on the surface and start to di use into the bulk of the substrate. The presence of precovered H（a） and O（a） has a signi cant effect on the adsorption and decomposition behavior of TMG. When the surface is pre-covered by saturated H2, CH4, and H2 desorptions are mainly observed at 315 K, which is ascribed to the dissociation of GaCH3 intermediate. In the case of O-precovered surface, the dissociation mostly occurs at 258 K, of which a Pd-O-Ga（CH3）2 structure is assumed to be the precusor. The presented results may provide some insights into the mechanism of surface reaction during the lm deposition by using trimethylgallium as precursor.

Modification of Surface Reactivity by CO： Effects on Decomposition and Polymerization of Acetaldehyde on Ru（0001）

The adsorption and reaction of acetaldehyde on the clean and CO pre-covered Ru（0001） surfaces have been investigated using temperature programmed desorption method. On the clean Ru（0001） surface, the decomposition of acetaldehyde is the main reaction channel, with little polymerization occurring. However, on the CO pre-covered Ru（0001） surface, the de- composition of acetaldehyde is inhibited considerably with increasing CO coverage. Whereas, the polymerization occurs efficiently, especially at high CO coverage （θco〉0.5 ML）, which is strongly CO coverage dependent. Combined with previous studies, the well-ordered hexagohal structure of CO layer formed on the Ru（0001） surface at high CO coverage that matches the configuration of paraldehyde is likely to be the origin of this remarkable phenomenon.

Surface Acidity of Aluminum Phosphate and Its Catalytic Performance in Benzene Alkylation with Long Chain Olefin

The acidic properties of aluminum phosphate （A1PO4-5） solid acid catalyst were characterized by tem- perature programmed desorption （TPD） of ammonia （NH3）, n-propylamine （n-C3HTNH2）, iso-propylamine [（CH3）2CHNH2] and n-dipropylamine [（C3H7）2NH] separately, and its catalytic performance in benzene alkylation with long chain olefin was studied in a fixed-bed reactor. The characterized acid amount of catalyst increased with the basicity of adsorbates. With increase of the activation temperature of catalyst, the acid amount characterized by NHa-TPD decreased, however, it increased when characterized by TPD using three other adsorbates. The desorption kinetics of TPD process and the deactivation kinetics of catalyst were investigated. The acidity and catalytic per- formance of catalyst was also correlated. The results showed that the acid amount and strength are well correlated with the activity and stability using NH3 as adsorbate, respectively, which indicated NH3 was a better basic adsorbate. It was also found that the catalyst with higher acid amount and lower acid strength on the surface exhibited the better catalytic performance and stability.

Effect of cobalt loading on reducibility, dispersion and crystallite size of Co/Al_2O_3 Fischer-Tropsch catalyst

Co/Al2O3 Fischer-Tropsch synthesis catalysts with different cobalt loadings were prepared using incipient wetness impregnation method. The effects of cobalt loading on the properties of catalysts were studied by means of X-ray diffraction （XRD）, temperature programmed reduction （TPR）, hydrogen temperature programmed desorption （H2-TPD） and O2 titration. Co-support compound formation can be detected in catalyst system by XRD. For the Co/Al2O3 catalysts with low cobalt loading, CoAl2O4 phase appears visibly. Two different reduction regions can be presented for Co/Al2O3 catalysts, which belong to Co3O4 crystallites （reduction at 320 ℃） and cobalt oxide-alumina interaction species （reduction at above 400 ℃）. Increasing Co loading results in the increase of Co3O4 crystallite size. The reduced Co/Al2O3 catalysts have two adsorption sites, and cobalt loading greatly influences the adsorption behavior. With the increase of cobalt loading, the amount of low temperature adsorption is increased, the amount of high temperature adsorption is decreased, and the percentage reduction and cobalt crystallite size are increased.

Effect of x-alumina addition on H_2S oxidation properties of pure and modified y-alumina

The influence of the textural and acidic properties ofγ‐Al2O3,(γ+χ)‐Al2O3,and?‐Al2O3on the catalytic activity,selectivity,and stability of direct H2S oxidation has been studied.A comparison of the H2S‐to‐S conversion effectiveness of aluminas with their acidic properties(identified by Fourier transform infrared spectroscopy and temperature programmed desorption of NH3)shows that H2S adsorption occurs predominantly on weak Lewis acid sites(LAS).γ‐Alumina samples containing aχ‐phase and/or modified Mg2+ions have a greater concentration of weak LAS and exhibit greater catalytic activity.When alumina is treated with a sulfuric acid solution,strong LAS appear and the number of LAS decreases significantly.Modification of alumina with hydrochloric acid has a limited effect on LAS strength.Weak LAS are retained and double in number compared to that present in the unmodified alumina,but the treated sample has Al?Cl bonds.Alumina samples modified by sulfate and chloride anions exhibit poor catalytic activity in H2S oxidation.

Effects of Surface Defects on Adsorption of CO and Methyl Groups on Rutile TiO_(2)(110)

The interaction of reactants with catalysts has always been an important subject for catalytic reactions.As a promising catalyst with versatile applications,titania has been intensively studied for decades.In this work we have investigated the role of bridge bonded oxygen vacancy(O_(v))in methyl groups and carbon monoxide(CO)adsorption on rutile TiO_(2)(110)(R-TiO_(2)(110))with the temperature programmed desorption technique.The results show a clear different tendency of the desorption of methyl groups adsorbed on bridge bonded oxygen(O_(b)),and CO molecules on the five coordinate Ti^(4+)sites(Ti_(5c))as the Ovconcentration changes,suggesting that the surface defects may have crucial influence on the absorption of species on different sites of R-TiO_(2)(110).

Suppression of Photoinduced BBO Defects Generation on TIO2（110） by Water

We have investigated creation of variable concentrations of defects on TIO2（110）-（1×1） surface by 266 nm laser using temperature programmed desorption technique. Oxygen-vacancy defects can be easily induced by ultraviolet light, the defects concentration has a linear dependence on power density higher than 50 mW/cm2 for 90 s irradiation. No observation of O2 molecule and Ti atom desorption suggests that UV induced defects creation on TiO2（110）-（1×1） is an effective and gentle method. With pre-dosage of thin films of water, the rate of defects creation on TiO2（110）-（1×1） is slower at least by two orders of magnitude than bare TiO2（110）-（1×1） surface. Further investigations show that water can be more easily desorbed by UV light, and thus desorption of bridging oxygen is depressed.

Surface Photocatalysis-TPD Spectrometer for Photochemical Kinetics

A surface photocatalysis-TPD apparatus devoted to studying kinetics and mechanism of pho- tocatalytic processes with various signal crystal surfaces has been constructed. Extremely high vacuum （-0.2 nPa） in the ionization region is obtained by using multiple ultrahigh vacuum pumps. Compared with similar instruments built previously by others~ the H2, CH4 background in the ionization region can be reduced by about two orders of magnitude, and other residual gases in the ionization region can be reduced by about an order of magnitude. Therefore, the signal-to-noise ratio for the temperature programmed desorption （TPD） and time of flight （TOF） spectra is substantially enhanced, making experimental studies of pho- tocatalytic processes on surfaces much easier. In this work, we describe the new apparatus in detail and present some preliminary studies on the photo-induced oxygen vacancy defects on TiO2（110） at 266 nm by using the TPD and TOF methods. Preliminary results suggest that the apparatus is a powerful tool for studying kinetics and mechanism of photochemical processes.

N2O Decomposition Catalyzed by K＋-doped Bi0.02Co

K＋-doped Bi0.02Co was investigated as catalyst for N2O decomposition. It was found that the catalytic performance of the Bi0.02Co catalyst, which was prepared by coprecipitation method, can be effectively modified by potassium cations via impregnation. The optimized K0.01Bi0.02Co catalyst exhibited much higher activity compared with Bi0.02Co and K0.01Co for the reaction in feed gas 0.2% N2O/Ar, irrespective of the presence or absence of impurity gas（volume fraction） 5%02, 2%H20, 0.12%NO and 10%CO2. Characterization of the catalysts with H2 temperature programmed reduction（H2-TPR） and O2 temperature programmed desorption（O2-TPD） indicate that the Co--O bond in Bi0.02Co was weakened by the K＋ doping, and hence the K0.01Bi0.02Co catalyst has much higher turnover frequency（TOF） than CO3O4 spinel and Bi0.02Co for the reaction.