메탄 건식 개질 반응에서 Ni/Al2O3의 촉매 거동에 대한 첨가제 및 CeO2 조촉매의 촉진 효과 규명

다국어 초록 (Multilingual Abstract)

The dry reforming of methane (DRM), a promising route for the simultaneous utilization of CH4 and CO2, requires catalysts that can maintain high activity and coke resistance under severe reaction conditions. In the first part of this study, the promotional effects of Ce, Mg, Si, and Ti on Ni/Al2O3 catalysts were systematically investigated to elucidate how each promoter alters the physicochemical properties relevant to DRM activity. XRD, BET, CO2-TPD, H2-TPR, and STEM–EDS analyses revealed that the promoters influenced the bulk structure, Ni–support interaction, reducibility, basicity, and coke formation behavior in distinct ways. Among them, Ce exhibited the most beneficial promotional effect by enhancing Ni reducibility, increasing CO2 adsorption through oxygen vacancies, and improving coke resistance via the oxygen storage capacity (OSC) of CeO2. Despite these advantages, significant catalyst deactivation was still observed, largely due to CeO2 particle growth after Ni incorporation, which diminished its OSC and impaired long-term stability. Motivated by these limitations, the second part of this work focuses on controlling CeO2 dispersion and strengthening Ni–support interaction using the hydrothermal versatility of ammonium aluminum carbonate hydroxide (AACH) –derived amorphous Al2O3. The AACH support exhibited a strong tendency to undergo hydrothermal transformation, which enabled the formation of Al-induced α-Ni(OH)2 during hydrothermal-assisted impregnation. This intermediate phase significantly promoted the formation of NiAl2O4 spinel during calcination, thereby enhancing the metal–support interaction even at high Ni loadings (20 wt%). Furthermore, combining hydrothermal support transformation with the co-impregnation of Ni and Ce precursors resulted in highly dispersed CeO2 domains, in contrast to the CeO2 aggregation observed in sequentially impregnated catalysts. The optimized co-impregnated catalyst (co.20Ni-Ce/A6W) exhibited stable Ni nanoparticles, highly dispersed CeO2, higher CO2 adsorption, and enhanced lattice oxygen mobility. These features suppressed the formation of refractory graphitic coke and favored the generation of easily oxidizable amorphous carbon, enabling outstanding long-term stability. In contrast, catalysts prepared by sequential impregnation suffered from rapid deactivation, severe graphitic carbon accumulation, and pronounced Ni sintering due to weak metal–support interactions and large CeO2 crystallites. Overall, this thesis demonstrates that (1) Ce is the most effective promoter for Ni/Al2O3 DRM catalysts among Ce, Mg, Si, and Ti, and (2) achieving highly dispersed CeO2 along with strong Ni–support interaction is essential for maximizing coke resistance and catalytic durability. By exploiting the hydrothermal versatility of AACH-derived alumina and employing a co-impregnation strategy, this work provides a new design principle for highly stable Ni-based DRM catalysts and offers mechanistic insights into how CeO2 dispersion, oxygen mobility, and interfacial metal–support interactions govern long-term catalyst performance.

목차 (Table of Contents)

• Ⅰ. 서론 1
• Ⅱ. 이론적 배경 3
• 1. 메탄 건식 개질(DRM) 반응의 특성 3
• 2. Ni/Al2O3 촉매의 특성과 한계 4
• 2.1. Ni/Al2O3 촉매의 구조적 특성 5
• 2.2. Ni 입자 크기에 따른 활성 및 코크 침적 경향 6
• 3. 조촉매(promoter)의 역할 및 필요성 7
• 3.1. 지지체의 열적 안정성 향상을 위한 조촉매 7
• 3.2. 표면 염기도 향상을 위한 조촉매 8
• 3.3. 산소 저장능을 활용한 산화적 코크 제거 조촉매 8
• 4. CeO2 조촉매의 구조적 특성과 역할 9
• 4.1. CeO2 결정 크기와 OSC의 상관관계 9
• 4.2. Al2O3 지지체 위에서의 CeO2 분산 및 미세화 전략 9
• Ⅲ. Ce, Mg, Si, Ti 조촉매가 Ni/Al2O3 촉매의 DRM 반응 성능에 미치는 영향 11
• 1. 실험 11
• 1.1. 시약 및 재료 11
• 1.2. 촉매 합성 11
• 1.3. 촉매 특성 분석 12
• 1.4. 촉매 성능 평가 13
• 2. 결과 및 고찰 15
• 2.1. Al 및 P-Al 지지체 특성 분석 15
• 2.2. Ni/P-Al 촉매의 특성 분석 21
• 2.3. 메탄 건식 개질 반응 촉매 성능 평가 34
• 2.4. 반응 후 촉매의 특성 분석 37
• 3. 결론 44
• Ⅳ. 합성 방법에 기반한 CeO2 및 Ni 분산 조절로 향상된 Ni-Ce/Al2O3 촉매의 DRM 특성 45
• 1. 실험 45
• 1.1. 시약 및 재료 45
• 1.2. 촉매 합성 45
• 1.3. 촉매 특성 분석 48
• 1.4. 촉매 성능 평가 48
• 2. 결과 및 고찰 49
• 2.1. AACH 유래 Al2O3의 수열 상전이 거동이 금속-지지체 상호작용에 미치는 영향 50
• 2.2. Co-impregnation과 Al2O3의 수열 변성이 CeO2 분산에 미치는 영향 61
• 2.3. 환원 후 촉매 분석 66
• 2.4. DRM 반응 성능 평가 71
• 2.5. 반응 후 촉매 분석 75
• 3. 결론 82
• Ⅴ. 요약 83
• Ⅵ. 향후 연구 85
• 참고문헌 87