LNG 촉매연소의 촉매 활성에 대한 팔라듐 담지

알루미나 촉매의 증진제 첨가에 의한 영향

이정운, 유승준*, 김선기, 홍승태,

황운연, 박형상, 박달령**, 윤호성***

서강대학교 공과대학 화학공학과

서남대학교 공과대학 환경화학공학부*

한국가스공사 연구개발원 이용기기연구실**

한국지질자원연구원 자원활용 연구부***

Effects of Addition of Promoter to Pd/Al2O3 Catalysts

on Catalytic Activity For LNG Catalytic combustion

J. W. Lee, S. J. Yoo*, S. K. Kim, S. T. Hong,

U. Y. Hwang, H. S. Park, D. R. Park** and H.-S. Yoon***

Dept. of Chem. Eng., Sogang University

*Faculty of Env. and Chem. Eng., Seonam University

**Gas R&D Center, Division of Gas Util., Korea Gas Corporation

***Div. of Min. Util., Korea Institute of Geoscience & Mineral Resources

1. Introduction

The catalytic combustion of hydrocarbons may provide an environmentally acceptable means of generating power without the associated problem of nitrogen oxides production.

In the last decades catalytic combustors for natural gas fueled gas turbine have attracted increasing attentions. Especially LNG is regarded as a future clean energy. It is possible if catalysts can endure at severe conditions(high temperature, water condition and etc.).

Catalytic combustors can conveniently be considered as low throughput systems(catalytic heaters, catalytic boilers, car exhaust systems) or high throughput units(catalytic gas turbines). We aimed that it can used the catalyst for gas  turbine at high temperature(Ｂ1300℃).  The thermal stability of the support material is an important design constraint.

The catalytic oxidation is dependent on factors such as the oxygen : methane feed ratio, the loading of precious metal on the support, the nature of the support, the particle size of the precious metal and the extent and nature of catalyst pretreatment.[4] we are focusing on the catalytic activity and heat resistance of support at high temperature.[1-5]

We should try to manufacture stable Pd encapsulation composite oxides catalysts on high temperature catalytic combustion above 1300℃. And we should establish the condition of a optimum catalyst preparation for the improvement of durability and high activity.

2. Experimental

Materials. The aluminum iso-propoxide(97）), palladium chloride hydrate(99.95）), tetraethyl orthosilicate(98）), barium nitrate hydrate(98.5）) and etc. by Sigma-Aldrich chemical Co. All materials were used without further purification. All solutions were prepared with triple distilled water.

Apparatus and procedure.  Aluminum isopropoxide was used as an alkoxide precusor. We manufactured boehmite(□-AlO(OH)) sol, as a intermediate, through the hydrolysis and polycondensation. After aging and peptization, then we added promoter and active component in order.

The catalyst was prepared by an encasulation method using palladium chloride hydrate powder containing 0.5wt）(Pd/Al).

Promoter-modified catalysts were dried overnight at 110℃. Then catalysts were sintered at various temperature(1100, 1200 and 1300℃) for high-temperature catalytic combustion.

Combustion tests have been performed using a quartz microreactor(ID:12mm) equipped with a sliding thermocouple loaded with 02-2g of powder catalyst with small particle size(dp＠3mm). The hydrocarbon conversion in the effluent gas was analyzed by on-line gas chromatography with a haysep D column.

3. Results and Discussion

The purpose of the present work two-fold. One objective was to provide a more complete picture of the stabilising properties of alumina relative to silica and to in clude other rare earth and alkaline earth ions in the comparision. Secondly, the work was designed to investigate the formation of mixed surface phases and their influence on the concentration and type of surface hydroxyl groups present.[6]

The presence of the rare-earth element decreases both the initial mean size of platinum crystallites and the extent of sintering of the supported metal after high-temperature treatments under various atmospheres.

Several promoters such as Si, La and rare-earth oxides will add to the alumina sol for high-temperature stability. And we will investigate the optimum condition of stable support such as amount of addition and condition of addition for the preparation of the best high-temperature stability.

Fig. 1 shows BET surface area of Pd/composite-alumina particles calcined at various temperatures. The surface area of Si is more than that of alkali earth metals and rare earth metals at 1200℃. But at 1300℃, all elements are similar. We need to investigate the correlation between surface area and catalytic activity of methane.

Fig. 2 shows the relation between conversion of CH4 and temperature of Pd/Ba-Al2O3 catalyst bed. The oxidation activity increased with a rise in reaction temperature. An enhancement of catalytic activity at lower temperature was achieved according to the space velocity decrement from 55,000 to 5,500h-1.

4. Conclusion

Sintering of alumina requires material transport on the solid state. This may proceed via bulk diffusion or surface diffusion.

The loss of surface area on heating may also be caused by the phase transformation of gamma alumina to alpha alumina. This requires a change in oxygen anion lattice from cubic to hexagonal close packed and results in a full recrystallisation, with a large change in surface area.

Finally when speaking about additon of active component, we should need to compare with catalytic activity of catalyst prepared impregantion and encapsulation method.

5. Reference

1. Bernard Beguin, Edouard Garbowski and Michel Primet, Appl. Catal., 75,      119(1991)

2. D. L. Trimm, Appl. Catal., 7, 249(1983)

3. Joo H. Lee and David L. Trimm, Fuel Proc. Tech., 42, 339(1995)

4. G. Groppi, C. Cristiani, L. Lietti, C. Ramella, M. Valentini and P. Forzatti,     Catalysis Today, 50, 399(1999)

5. H. Schaper, E. B. M. Doesburg and L. L. Van Reijen, Appl. Catal., 7,          211(1983)

6. Jeffrey S. Church, Noel W. Cant and David L. Trimm, Appl. Catal. A, 101,     105(1993)

Fig. 1. BET surface area of Pd/       Fig. 2. Dependence of CH4 combustion

composite-alumina particles             over pd/Ba-Al2O3 catalysts on

calcined at various temperatures.        reaction temperature according to                                             the space velocity.