Ethylene glycol dry reformingfor syngas production over co/al2o3 catalysts / Lau Ngie Jun

Faculty of Chemical and Process Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2020

Includes bibliographical references

Ethylene glycol dry reforming (EGDR) is emerging as a new alternative route for converting renewable ethylene glycol (C2H6O2) and carbon dioxide (CO2) to syngas. However, the dry reforming reaction is typically accompanied by coke deposition that leads to catalyst deactivation. Therefore, the development of superior catalyst with the desirable activity and stability is an imperative task. This thesis had investigated the physicochemical attributes of 10%Co/Al2O3 and evaluated the effects of promoter (Ce and La) and reaction temperatures (923–998 K) on the catalytic activity of EGDR reaction in a quartz fixed-bed reactor. The 10%Co/Al2O3 was successfully prepared using the incipient wetness impregnation method. The characterization of fresh catalysts (10%Co/Al2O3, 3%Ce-10%Co/Al2O3 and 3%La-10%Co/Al2O3) showed that the BET surface area decreased after the addition of promoter. The addition of promoter decreased the Co3O4 crystallite size from 21.4 nm to 9.2 nm and 9.8 nm for 3%Ce-10%Co/Al2O3 and 3%La-10%Co/Al2O3, respectively. The XRD patterns showed the presence of Co3O4 and CoAl2O4 phases, and this result was consistent with the result obtained from the peak assignments in H2-TPR measurement. The La2O3 phase was not detected in XRD, probably because it was finely dispersed in catalyst. Irrespective of reaction conditions, La-promoted catalyst seemed to be an optimum catalyst in terms of both C2H6O2 and CO2 conversions. Reactant conversions of catalysts increased in the following order: 10%Co/Al2O3 < 3%Ce-10%Co/Al2O3 < 3%La-10%Co/Al2O3 for all operating conditions. For 3%La-10%Co/Al2O3, C2H6O2 and CO2 conversions increased up to 77.6% and 43.1%, with increasing reaction temperature from 923 to 998 K due to the endothermic character of EGDR reaction. The effect of La loadings (1%, 3% and 5%) revealed that the optimal La loading was attained at 3% La owing to the smaller metal particle size, lower reduction temperature of metal, and homogeneous metal distribution. 3%La-10%Co/Al2O3 was further tested to identify the effects of feed ratios (C2H6O2:CO2 = 1:1‒1:2.5 and 1:1‒2.5:1; equivalent with C2H6O2:CO2 (kPa) = 15:15‒15:37.5 and 15:15‒37.5:15) and reaction temperatures (923‒998 K). At moderate reaction temperatures (923-973 K), an increase in CO2 partial pressure from 15 to 30 kPa resulted in an increase in C2H6O2 conversion, which then slightly decreased at elevated CO2 partial pressure (37.5 kPa). Meanwhile, CO2 conversion was found to be responsive at high temperature (> 973 K) with increasing CO2 partial pressure. The significant change in activity was due to the existence of reverse Boudouard reaction which was initiated above 973 K. Low activity was observed at C2H6O2 partial pressure of 37.5 kPa and temperature of 923 K, with C2H6O2 and CO2 conversions being 38.0% and 7.7%, respectively. In EGDR runs, H2/CO ratio was always higher than the stoichiometric ratio (0.67) due to the presence of side reaction (ethylene glycol steam reforming). The spent 10%Co/Al2O3 and 3%La-10%Co/Al2O3 characterizations showed the heterogeneous nature of the deposited carbons (carbon nanofilament and graphite). However, the carbon nanofilament appeared as the dominant carbon on the surface of spent catalyst. The introduction of 3% La reduced the carbon formation from 96.6% to 82.0% due to the formation of La2O2CO3 intermediate phase that facilitates in carbon removal, showing improved catalytic performance of La-promoted catalyst as compared to unpromoted catalyst. This study successfully synthesized superior EGDR catalyst (3%La-10%Co/Al2O3) with interesting properties (smaller metal particle size, lower reduction temperature of metal, and homogeneous metal distribution), excellent activity (T = 998K, C2H6O2 conversion = 77.6%, CO2 conversion = 43.1%) and tolerate carbon formation.