일산화탄소와 이산화탄소의 메탄화반응용 담지된 니켈 촉매에 대한 연구
A study on supported Ni catalysts for CO and CO2 methanation
- 주제(키워드) Ni catalyst , CO , CO2 methanation
- 발행기관 아주대학교
- 지도교수 박은덕
- 발행년도 2019
- 학위수여년월 2019. 8
- 학위명 박사
- 학과 및 전공 일반대학원 에너지시스템학과
- 실제URI http://www.dcollection.net/handler/ajou/000000029256
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
Considering the CO2 emission rate, hydrogen may be the most suitable reactant to transform CO2 into value-added chemicals. Besides, CO from biomass or organic waste gasifiers can be used to produce synthetic natural gas. The CO and CO2 methanation reactions, called Sabatier reactions, are highly exothermic, a series of adiabatic reactors with intermediate heat exchangers are required to achieve high methane yields. In order to achieve high single-pass CO and CO2 conversions, these reactions should be performed at low temperatures using a reactor equipped with a heat exchanger, which requires a highly active catalyst. In this thesis, the supported Ni catalysts have been studied for CO and CO2 methanation process. It has been reported that the methanation activity of catalyst has been determined based on the metal dispersion, as well as the distribution of the strength and concentration of basic sites. At here, the investigation of a core-shell structural support in supported Ni catalyst systems via wet-impregnation (WI) and deposition-precipitation (DP) method was conducted. The application of Al@Al2O3 to Ni-based samples, which showed the remarkable methanation activity for both CO and CO2 methanation at low temperature. DP method with a mild thermal pretreatment is confirmed as the more effective preparation method to enhance the catalytic activity compared to the conventional WI method. The Ni/Al@Al2O3 synthesized by the DP method claimed the catalytic improvement and good stability during methanation reaction. Besides, several promoters (Mn, Ce, Zr, Mg, K, Zn, or V) were examined in order to improve the catalytic performance of promoted Ni catalysts. Mn, Ce, Mg, V, and Zr are beneficial for enhancing both CO and CO2 methanation activity due to the improvement in Ni dispersion and enhancement of CO2 adsorption capacity with strong interaction with the catalyst surface. The Ni-V/γ-Al2O3 catalyst showed the highest CO methanation activity because it had the largest Ni sites; however, its CO2 methanation activity was low owing to the small amount of adsorbed CO2. Between the promoters, the effect of Mn on both CO and CO2 methanation was the most remarkable. However, both K and Zn were observed to have a negative effect on both CO and CO2 methanation due to their blockage of active Ni sites and the decrease in the number of basic sites. Moreover, Ni/SiO2 catalysts with high Ni content were prepared from aqueous Ni(NO3)2 solutions by the precipitation method using Na2SiO3 as a silica precursor and precipitant. This is a simple but efficient method to prepare well-dispersed NiO on silica, which can be further transformed to Ni/SiO2 through an additional reduction process. The prepared catalyst showed significantly enhanced performance for CO methanation compared to core-shell Ni@SiO2 catalysts and conventional Ni/SiO2 catalysts prepared by WI. The new kind of core-shell support, the unique core-shell aluminate spinel - Al@M(M = Zn, Mg, or Mn)Al2O4, were obtained by simple hydrothermal surface oxidation (HTSO) and applied to the preparation of supported Ni catalysts. The combination of core-shell spinel structural supports and the Ni doping with DP method made the outstanding catalytic performance of Ni/Al@MgAl2O4 and Ni/Al@MnAl2O4 samples due to the improvement of the dispersion of Ni nanoparticles and the creation of moderate basic sites with suitable strength. The good stability of Ni/Al@MnAl2O4 catalysts was also confirmed.
more목차
ABSTRACT i
TABLES OF CONTENT iii
LIST OF TABLES vi
LIST OF FIGURES viii
CHAPTER I. INTRODUCTION 1
1.1. Motivation ............................................................................................................ 1
1.2. Methanation catalyst ............................................................................................ 4
1.2.1. Ni-based catalyst .............................................................................................. 4
1.2.2. Support ............................................................................................................. 9
1.2.3. Promoter ........................................................................................................... 9
1.2.4. Fabrication method ........................................................................................... 11
1.3. Challenges in methanation catalyst ..................................................................... 12
1.3.1. Overcoming the catalyst deactivation............................................................... 12
1.3.2. Highly active and stable catalysts at low temperature ...................................... 18
CHAPTER II. EXPERIMENTAL 19
2.1. Catalyst fabrication .............................................................................................. 19
2.1.1. Ni/Al@Al2O3 catalysts preparation .................................................................. 19
2.1.2. Promoted Ni-M/Al@Al2O3 catalysts preparation ............................................. 22
2.1.3. Preparation of Ni/SiO2 catalyst with high Ni content ....................................... 22
2.1.4. Ni/Al@M(M = Zn, Mg, or Mn)Al2O4 catalysts preparation ............................ 26
2.2. Catalyst characterization ..................................................................................... 27
2.3. Catalytic activity evaluation ................................................................................ 31
CHAPTER III. RESULTS AND DISCUSSION 33
3.1. Ni/Al@Al2O3 catalyst .......................................................................................... 33
3.1.1. Characterization of Ni/Al@Al2O3 catalysts ..................................................... 33
3.1.2. CO methanation ................................................................................................ 43
3.1.3. CO2 methanation .............................................................................................. 48
3.1.4. CO2 methanation mechanism ........................................................................... 53
3.1.5. Stability evaluation ........................................................................................... 58
3.2. Effect of promoters on promoted Ni-M/Al@Al2O3 catalysts .............................. 64
3.2.1. Characterization of promoted Ni-M/Al@Al2O3 catalysts ................................ 64
3.2.2. CO methanation ................................................................................................ 75
3.2.3. CO2 methanation .............................................................................................. 81
3.2.4. In-situ DRIFTS study ....................................................................................... 86
3.2.5. Stability ............................................................................................................ 87
3.3. Facile fabrication of Ni/SiO2 with high Ni content ............................................. 91
3.3.1. Characterization of the Ni/SiO2 catalysts ......................................................... 91
3.3.2. CO methanation ................................................................................................ 108
3.4. Ni/Al@M(M=Zn, Mg, or Mn)Al2O4 catalysts .................................................... 115
3.4.1. Characterization of Ni/Al@MAl2O4 catalysts .................................................. 115
3.4.2. Catalytic methanation performance .................................................................. 131
CHAPTER IV. CONCLUSIONS 143
REFERENCES 145
PUBLICATIONS 155
ACKNOWLEDGMENT 156
