Preparation and Reactivity of Cu-Zn-Al Based Hybrid Catalysts for Direct Synthesis of Dimethyl Ether by Physical Mixing and Precipitation Methods

Two hybrid catalysts for the direct synthesis of DME were prepared and the catalytic activity of these catalysts were investigated. The hybrid catalyst for the direct synthesis of DME was composed as the catalytic active components of methanol synthesis and dehydration. The methanol synthesis catalyst was formed from the precursor contained Cu and Zn, the methanol dehydration catalyst was used ${\gamma}-Al_2O_3$. As PM-CZ+D and CP-CZA/D, Two hybrid catalysts were prepared by physical mixing method (PM-CZ+D) and precipitation method (CP-CZA/D), respectively. PM-CZ+D was prepared by physically mixing methanol synthesis catalyst and methanol dehydration catalyst, CP-CZA/D was prepared by depositing Cu-Zn or Cu-Zn-Al components on ${\gamma}-Al_2O_3$. The crystallinity and the surface morphology of synthesized catalyst were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) to investigate the physical property of prepared catalyst. And BET surface area by $N_2$ adsorption and the surface area of Cu by $N_2O$ chemisorption were investigated about the hybrid catalysts. In addition, catalytic activity of these hybrid catalysts was examined with varying reaction conditions. At that time, the reaction temperature of $250{\sim}290^{\circ}C$, the reaction pressure of 50~70 atm, the $[H_2]/[CO]$ mole ratio of 0.5~2.0 and the space velocity of $1,500{\sim}6,000h^{-1}$ were investigated the catalytic activity. From these results, it was confirmed that the reactivity of CP-CZA/D was higher than that of PM-CZ+D. When the conditions of reaction temperature, pressure, $[H_2]/[CO]$ ratio and space velocity were $260^{\circ}C$, 50 atm and 1.0, $3,000h^{-1}$ respectively, CO conversion using CP-CZA/D hybrid catalyst was 72% and the CO conversion of CP-CZA/D was more than 20% compared with the CO conversion of PM-CZ+D. It was known that Cu surface area of CP-CZA/D hybrid catalyst was higher than that of hybrid PM-CZ+D catalyst using $N_2O$ chemisorption. It was assumed that the catalytic activity was improved because Cu particle of hybrid catalyst prepared by precipitation method was well dispersed.

물리혼합 및 침전법에 의한 DME 직접 합성용 Cu-Zn-Al계 혼성촉매의 제조 및 반응특성

본 연구에서는 DME 직접 합성을 위한 혼성촉매가 두 가지 방법으로 제조되었으며, 이들의 촉매적 활성이 조사되었다. DME 합성을 위한 혼성촉매는 메탄올 합성과 메탄올 탈수반응에 촉매적 활성을 가진 성분들로 제조되었다. 메탄올 합성촉매는 Cu와 Zn이 함유된 전구물질로부터 합성되었으며, 메탄올 탈수촉매는 ${\gamma}-Al_2O_3$를 이용하였다. 두 촉매는 물리혼합법과 침전법에 의해서 혼성촉매로 제조되었다. 물리혼합법은 두 촉매를 분말상태에서 혼합하는 것이며, 침전법은 ${\gamma}-Al_2O_3$ 촉매상에 Cu-Zn 또는 Cu-Zn-Al 성분을 퇴적시키는 방법이다. 제조된 촉매의 물리적 특성을 조사하기 위하여 X선 회절법에 의한 결정구조, 질소흡착에 의한 BET 표면적, $N_2O$ 화학흡착에 의한 Cu의 표면적 그리고 주사전자현미경에 의한 표면형상 등이 조사되었다. 또한 이들 혼성촉매의 촉매적 활성은 여러 가지 반응조건을 변화시키면서 조사되었다. 이때 반응온도는 $250{\sim}290^{\circ}C$, 반응압력은 30~70 atm, $[H_2]/[CO]$ 몰비는 0.5~2.0, 그리고 공간속도는 $1,500{\sim}6,000 h^{-1}$ 촉매활성이 조사되었다. 반응성 실험 결과로부터 침전법으로 제조된 혼성촉매(CP-CZA/D)가 물리혼합법으로 제조된 혼성촉매(PM-CZ+D)보다 우수한 반응성을 나타냄을 확인할 수 있었으며, 특히 반응 온도, 압력, $[H_2]/[CO]$ 비, 공간속도가 각각 $260^{\circ}$, 50 atm, 1.0, $3,000h^{-1}$인 조건에서 침전법에 의해 제조된 촉매의 CO 전화율이 72%로 물리혼합법으로 제조된 촉매보다 약 20% 이상 높았다. $N_2O$ 화학흡착실험으로부터 Cu 표면적을 측정한 결과, PM-CZ+D 혼성촉매보다 CP-CZA/D 혼성촉매의 Cu 표면적이 더 높았다. 그러므로 침전법으로 제조된 혼성촉매상의 Cu입자가 더 잘 분산되었기 때문에 촉매의 활성이 개선된 것으로 판단된다.