Deactivation of Ni-Al-Based Catalysts for Autothermal Reforming of Diesel Surrogate Fuel in the Presence of an Aromatic Hydrocarbon.

Diesel fuel can produce higher concentrations of H2 and CO gases than other types of hydrocarbon fuels via a reforming reaction for solid oxide fuel cells (SOFCs). However, in addition to sulfur compounds and aromatic hydrocarbons in diesel fuel are a major cause of catalyst deactivation. To elucidate the phenomenon of catalyst deactivation in the presence of an aromatic hydrocarbon, dodecane (C12H26) and hexadecane (C16H34) were blended with an aromatic hydrocarbon such as 1-methylnaphthalene (C11H10) to obtain a diesel surrogate fuel. The experiments were performed for autothermal reforming of the diesel surrogate fuel under conditions of S/C = 1.17, O2/C = 0.24, 750°C and GHSV= 12,000 h-1. Three Ni-Al-based catalysts with 10 wt% (N10A), 30 wt% (N30A) and 50 wt% (N50A) of NiO were prepared via the polymer modified incipient method. Whereas all of the Ni-Al-based catalysts were deactivated with increasing reaction time, the catalysts with greater Ni contents tended to maintain their catalytic performance for a longer time. Correlation between the catalytic performances and Ni content were analyzed by temperature-programmed reduction (TPR), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX), Brunauer-Emmett-Teller(BET) analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Also, we concluded that ethylene (C2H4), which was detected by gas chromatography-mass spectrometry (GC-MS), was the fundamental cause of deactivation of the Ni-Al-based catalysts by accelerating the deposition of wire-type carbon on the catalytic surface.

Effects of Thin-Film Thickness on Sensing Properties of SnO2-Based Gas Sensors for the Detection of H2S Gas at ppm Levels.

SnO2 thin-film gas sensors were easily created using the ion sputtering technique. The as-deposited SnO2 thin films consist of a tetragonal SnO2 phase and densely packed nanosized grains with diameters of approximately 20-80 nm, which are separated by microcracks. The as-deposited SnO2 thin film is well crystallized, with a dense columnar nanostructure grown directly onto the alumina material and the Pt electrodes. The grain size and thickness of SnO2 thin films are easily controlled by varying the sputtering time of the ion coater. The responses of the SnO2 thin-film sensors decrease as the SnO2 film thickness is increased, indicating that a negative association exists between the sensor response and the SnO2 film thickness due to gas diffusion from the surface. The SnO2 thin-film sensor, which was created by ion sputtering for 10 min, shows an excellent sensor response (Ra/Rg where Ra is the electric resistance under air and Rg is the electric resistance under the test gas) for detecting 1 ppm H2S at 350°C.

Improvement of H2S sensing properties of SnO2-based thick film gas sensors promoted with MoO3 and NiO.

The effects of the SnO2 pore size and metal oxide promoters on the sensing properties of SnO2-based thick film gas sensors were investigated to improve the detection of very low H2S concentrations (<1 ppm). SnO2 sensors and SnO2-based thick-film gas sensors promoted with NiO, ZnO, MoO3, CuO or Fe2O3 were prepared, and their sensing properties were examined in a flow system. The SnO2 materials were prepared by calcining SnO2 at 600, 800, 1,000 and 1,200 °C to give materials identified as SnO2(600), SnO2(800), SnO2(1000), and SnO2(1200), respectively. The Sn(12)Mo5Ni3 sensor, which was prepared by physically mixing 5 wt% MoO3 (Mo5), 3 wt% NiO (Ni3) and SnO2(1200) with a large pore size of 312 nm, exhibited a high sensor response of approximately 75% for the detection of 1 ppm H2S at 350 °C with excellent recovery properties. Unlike the SnO2 sensors, its response was maintained during multiple cycles without deactivation. This was attributed to the promoter effect of MoO3. In particular, the Sn(12)Mo5Ni3 sensor developed in this study showed twice the response of the Sn(6)Mo5Ni3 sensor, which was prepared by SnO2(600) with the smaller pore size than SnO2(1200). The excellent sensor response and recovery properties of Sn(12)Mo5Ni3 are believed to be due to the combined promoter effects of MoO3 and NiO and the diffusion effect of H2S as a result of the large pore size of SnO2.

Effects of textural properties on the response of a SnO2-based gas sensor for the detection of chemical warfare agents.

The sensing behavior of SnO(2)-based thick film gas sensors in a flow system in the presence of a very low concentration (ppb level) of chemical agent simulants such as acetonitrile, dipropylene glycol methyl ether (DPGME), dimethyl methylphosphonate (DMMP), and dichloromethane (DCM) was investigated. Commercial SnO(2) [SnO(2)(C)] and nano-SnO(2) prepared by the precipitation method [SnO(2)(P)] were used to prepare the SnO(2) sensor in this study. In the case of DCM and acetonitrile, the SnO(2)(P) sensor showed higher sensor response as compared with the SnO(2)(C) sensors. In the case of DMMP and DPGME, however, the SnO(2)(C) sensor showed higher responses than those of the SnO(2)(P) sensors. In particular, the response of the SnO(2)(P) sensor increased as the calcination temperature increased from 400 °C to 800 °C. These results can be explained by the fact that the response of the SnO(2)-based gas sensor depends on the textural properties of tin oxide and the molecular size of the chemical agent simulant in the detection of the simulant gases (0.1-0.5 ppm).

Development of regenerable MgO-based sorbent promoted with K2CO3 for CO2 capture at low temperatures.

To improve their CO2 absorption capacity, alkali-based sorbents prepared by impregnation and wet mixing method of potassium carbonate on supports such as activated carbon and MgO (KACI30, KACP30, KMgI30, and KMgP30), were investigated in a fixed bed reactor (C02 absorption at 50-100 degrees C and regeneration at 150-400 degrees C). Total CO2 capture capacities of KMgI30-500 and KMgP30-500 were 178.6 and 197.6 mg CO2/g sorbent, respectively, in the presence of 11 vol % H2O even at 50 degrees C. The large amount of CO2 capture capacity of KMgP30-500 and KMgI30-500 could be explained by the fact that MgO itself, as well as K2CO3, could absorb CO2 in the presence of water vapor even at low temperatures. In particular, water vapor plays an important role in the CO2 absorption of MgO and KMgI30-500 even at low temperatures below 60 degrees C, in marked contrast to MgO and CaO which can absorb CO2 at high temperatures. The CO2 capture capacity of the KMgI30-300 sorbent, however, was less than that of KMgI30-500 due to the formation of Mg(OH)2 which did not absorb CO2. MgO based-sorbents promoted with K2CO3 after CO2 absorption formed new structures such as K2Mg(CO3)2 and K2Mg(CO3)2 x 4(H2O), unlike KACI30 which showed only the KHCO3 crystal structure. The new Mg-based sorbents promoted with K2CO3 showed excellent characteristics in that it could satisfy a large amount of CO2 absorption at low temperatures, a high CO2 absorption rate, and fast and complete regeneration.