• Journal of Applied Reliability
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• v.6 no.1
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• pp.37-50
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• 2006

The accelerated life tests of the catalytic gas sensor were performed at three different gas concentration conditions. From the test data, the power-Weibull model was estimated and the acceleration factor between test condition 25%LEL(Lowe Explosive Limit) and use condition 5%LEL was about 3 according to this acceleration model. Using this acceleration factor, life test specification for qualifying that B10 lifetime of the catalytic gas sensor meets the goal lifetime (5 years) was designed.

• Bulletin of the Korean Chemical Society
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• v.29 no.2
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• pp.339-341
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• 2008

Catalytic trimerization of isobutene to produce triisobutenes has been performed over cation-exchange resin and zeolite catalysts. Resin catalysts have the advantage of long lifetime and high trimers selectivity even though the regeneration of an aged catalyst is not satisfactory. On the contrary, zeolite catalysts can be regenerated facilely by simple calcination in air even though the lifetime is short and trimers selectivity is low probably due to small pore size and strong acidity, respectively. It is, therefore highly desirable to develop an inorganic acid catalyst with macro- or meso-pores to show catalytic performances similar or superior to those of macroporous resin catalysts.

• Applied Chemistry for Engineering
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• v.34 no.5
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• pp.548-555
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• 2023

SAPO-34 catalysts were modified with polyethylene glycol (PEG) and Pb to improve their catalytic lifetime and selectivity for light olefins in the conversion of dimethyl ether to olefins (DTO). Hierarchical SAPO-34 catalysts and PbAPSO-34 catalysts were synthesized according to changes in the molecular weight of PEG (M.W. = 1000, 2000, 4000) and the molar ratio of Pb/Al (Pb/Al = 0.0015, 0.0025, 0.0035), respectively. By introducing PEG into the SAPO-34 catalyst crystals, an enhanced volume of mesopores and reduced acidity were observed, resulting in improved catalytic performance. Pb was successfully substituted into the SAPO-34 catalyst frameworks, and an increased BET surface area and concentration of acid sites in the PbAPSO-34 catalysts were observed. In particular, the concentrations of the weak acid sites, which induce a mild reaction, were increased compared with the concentrations of strong acid sites. Then, the P2000-Pb(25)APSO-34 catalyst was prepared by simultaneously utilizing the synthesis conditions for the P2000 SAPO-34 and Pb(25)APSO-34 catalysts. The P2000-Pb(25)APSO-34 catalyst showed the best catalytic lifetime (183 min based on DME conversion > 90%), with an approximately 62% improvement compared to that of the unmodified catalyst (113 min).

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.319-319
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• 2011

Hydrolysis of sodium borohydride provides a safe and clean approach to hydrogen generation. Having the proper catalytic support for controlling this reaction is therefore a valuable technology. Here we demonstrate the capability of hydroxyapatite as a novel catalytic support material for hydrogen generation. Aside from being inexpensive and durable, we reveal that Ru ion exchange on the HAP surface provides a highly active support for sodium borohydride hydrolysis, exemplifying a high total turnover number of nearly 24,000 mol $H_2$/ mol Ru. Moreover, we observe that the RuHAP support exhibits a high catalytic lifetime of approximately one month upon repeated exposure to $NaBH_4$ solutions. In addition to examining surface area effects, we also identified the role of complex surface morphology in enhancing hydrolysis by the catalytic transition metal covered surface. Particularly, we found that a polycrystalline RuHAP catalytic support exhibits shorter induction times for the initial bubble formation as well as increased hydrogen generation rates as compared to a single crystal supports. The independent factor of a complex surface morphology is believed to provide enhanced sites for gas release during the initial stages of the reaction. By demonstrating the ability to shorten induction time and enhance catalytic activity through changes in surface morphology and Ru content, we find it feasible to further explore this catalyst support in the construction of a practical hydrogen generator.

• Applied Chemistry for Engineering
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• v.32 no.3
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• pp.305-311
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• 2021

Effects of chitosan as a mesopore directing agent of SAPO-34 catalysts were investigated to improve the catalytic lifetime in DTO reaction. The synthesized catalysts were characterized by XRD, SEM, N₂ adsorption-desorption isotherm and NH₃-temperature programmed desorption (TPD). The modified SAPO-34 catalysts prepared by varying the added amount of chitosan showed the same cubic morphology and chabazite structure as the conventional SAPO-34 catalyst. As the added amount of chitosan increased to 3 wt%, the surface area, mesopore volume and concentration of weak acid sites of modified SAPO-34 catalysts increased. The modified SAPO-34 catalysts showed enhanced catalytic lifetime and high selectivity for light olefins in the DTO reaction. In particular, the SAPO-CHI 3 catalyst (3 wt%) exhibited the longest catalytic lifetime than that of the conventional SAPO-34. Therefore, it was confirmed that chitosan was a suitable material as a mesopore directing agent to delay deactivation of the SAPO-34 catalyst.

• Journal of Korean Society on Water Environment
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• v.33 no.1
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• pp.34-39
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• 2017

Under a corrosive environment, electrodes that are applied in the water-treatment system need not only very high electrochemical activity for fast reactions, but also high durability for cost saving. Therefore, the fabrication condition of iridium electrodes was examined to produce a more durable iridium electrode in this study. Tantalum was selected as a binder to enhance the durability of the iridium electrode. Investigation of the weight ratio between the catalyst and the binder to improve electrochemical activity was performed. Also, to compare the effect of the different coating amounts of the catalyst, the results of CV (Cyclic Voltammetry) and EIS (Electrochemical Impedance Spectroscopy) were discussed. Furthermore, an ALT(Accelerated Lifetime Test) was designed and applied to the electrodes to determine the conditions for highly durable electrode fabrication.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.593-595
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• 1992

To improve the lifetime and output power in a sealed-off $CO_2$ laser, a series of Nd$_{1-x}$Sr$_x$CoO$_3$(x = 0.0, 0.25, 0.40, 0.50, 0.60, 0.75) perovskite-type compounds has been synthesized and used for a cathode material. Using a typical method samples were sintered at 1150$^{\circ}$C and their structures were determined as a cubic form by means of XRD analysis. The degrees of $CO_2$ dissociation were measured by PAS (photoacoustic spectroscopy) with the lapse of time. In the case of $Nd_{0.4}$Sr$_{0.6}$$CoO_3$, which showed the highest catalytic cathode effect, only 7% of the initial $CO_2$ concentration were dissociated at 30 torr of gas mixture and 5 mA of discharge current. The more the gas pressure decreased and the discharge current increased, the more the degree of dissociation occurred. The ability of catalytic cathode to regenerate CO$_2$ in the laser cavity lies in order for x, 0.60 > 0.50 > 0.40 > 0.75 > 0.25 ${\gg}$ 0.0. Except for the case of x = 0.0 the amounts of $CO_2$ dissociation were found to be within 7-15% of the initial $CO_2$ concentration.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.20-27
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• 2021

Effects of the etching treatment of SAPO-34 catalyst were investigated to improve the catalytic lifetime in DTO reaction. The aqueous NH3 solution was a more appropriate treatment agent which could control the degree of etching progress, compared to that of using a strong acid (HCl) or alkali (NaOH) solution. Therefore, the effect on characteristics and lifetime of SAPO-34 catalyst was observed using the treatment concentration and time of aqueous NH3 solution as variables. As the treatment concentration or time of aqueous NH3 solution increased, the growth of erosion was proceeded from the center of SAPO-34 crystal plane, and the acid site concentration and strength gradually decreased. Meanwhile, it was found that external surface area and mesopore volume of SAPO-34 catalyst increased at appropriate treatment conditions. When the treatment concentration and time were 0.05 M and 3 h, respectively, the lifetime of the treated SAPO-34 catalyst was the longest, and was significantly enhanced by ca. 36% (based on DME conversion of > 90%) compared to that of using the untreated catalyst. The model for the etching progress of SAPO-34 catalyst in a mild treatment process using aqueous NH3 solution was also proposed.

• Applied Chemistry for Engineering
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• v.26 no.2
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• pp.217-223
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• 2015

Effects of the post-acid treatment of SAPO-34 sample by hydrochloric acid were investigated to enhance the catalytic performance in DTO reaction. Uniformly sized SAPO-34 samples with cubic-like morphology were prepared by hydrothermal method using TEAOH and DEA as the structure directing agents. It was modified in terms of the HCl concentration and treating time. As a result, the total surface area and micropore volume for the well modified samples increased and the total acid site was somewhat decreased along with the erosion of the external surface. Especially, the catalytic lifetime and light olefins selectivity for acid treated SAPO-0.2 M (3 h) samples were considerably enhanced compared with those of untreated SAPO-34 samples. It indicates that the deactivation by coke formation proceeds mainly at the pore entrance on the external surface. Therefore, the acid treatment was confirmed to be a simple method which can significantly improve the catalytic performance by modifying the external surface of SAPO-34 catalyst.

• Applied Chemistry for Engineering
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• v.25 no.1
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• pp.34-40
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• 2014

Mesoporous SAPO-34 catalyst was successfully synthesized by the hydrothermal method using carbon nanotube (CNT) as a secondary template. The effects of CNT contents (0.5, 1.5, 2.5, and 4.5 mol%) on catalytic performances were investigated. The synthesized catalysts were characterized with XRD, SEM, nitrogen physisorption isotherm and $NH_3$-TPD. Among the synthesized catalysts, SAPO-34 catalyst prepared by the addition of 1.5 mol% CNT (1.5C-SAPO-34) observed not only the largest amounts of mesopore volume but also acid sites. However, the mesopore volume was relatively decreased by further increasing of CNT contents due to the formation of small crystalline. The catalytic lifetime and the selectivity of light olefins ($C_2{\sim}C_4$) were examined for the dimethyl ether to olefins reaction. As a result, the 1.5C-SAPO-34 catalyst showed an improvement of ca. 36% in a catalytic lifetime and a better selectivity to light olefins as compared with the general SAPO-34 catalyst.