Ce-promoted Co/SBA-15 synthesized from oil palm ash for dry reforming of methane / Hazirah A. Razak

Faculty of Chemical and Process Engineering Technology

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

Includes bibliographical references

Dry reforming of methane (DRM) is a greener approach as this pathway transforms two main greenhouse gases; methane and carbon dioxide into syngas (mixture of hydrogen and carbon monoxide). However, this process suffers from catalyst deactivation that is normally caused by active metal sintering and carbon formation. In the present study, mesoporous Silica Barbara Amorphous (SBA-15) has been the preferred support material that possesses high surface area (>600 m2/g), large pore diameter (5-30 nm), and thicker pore walls (3-6 nm). Commonly, the synthesis of SBA-15 required commercial tetraethylortho- silicate (TEOS) or sodium silicate (Na2SiO3) which is non-economical and noneco- friendly. Thus, this study focuses on the synthesis of SBA-15 using waste material Oil Palm Ash (OPA) as an alternative silica source. The extraction of sodium silicate-oil palm ash (Na2SiO3-OPA) was carried out using reflux method by varying the effect of NaOH concentration, extraction temperature, and extraction time. The optimum condition was achieved at NaOH concentration of 2.5 N, extraction temperature of 120 oC, and extraction time of 3 h with a maximum Na2SiO3-OPA concentration of 61021 ppm. The structural confirmation of SBA-15 from OPA was determined by low-angle XRD, BET, FTIR and TEM. The introduction of Ce promoter and Co active metal on SBA-15 support was investigated by the employing sol-gel (SG) method. The characterization and catalytic performance were carried out to affirm the effect of introduction Ce-promoted Co/SBA-15 (OPA). Three types of introduction of Ce promoter which are Ce loaded on the SBA-15 followed by Cobalt, Co loaded on the SBA-15 followed by Ce, and combined Co and Ce loaded on the SBA-15 were assigned as Co/Ce, Ce/Co, and Co-Ce. Co/Ce/SBA-15 (OPA) exhibited the highest catalytic activity in DRM due to the existence of basic CeO2 that creates more active sites of Co and influences the distribution of Co species on the SBA-15. The effect of Co loadings (3, 5, 7, and 10 wt.%) on Cebased SBA-15 (OPA) was also investigated. The TEM and FESEM-EDX images revealed that 7 wt.% exhibited a homogenous metal dispersion. Meanwhile, 10Co/Ce/SBA-15 (OPA) revealed agglomeration of Co species located at the external surface SBA-15 (OPA). It is notable that the optimal Co loading on Ce-based SBA-15 (OPA) strengthens metal-support interaction and generates small CoO crystallite size that led to an excellent performance towards dry reforming of methane. Moreover, the activation energy of 7Co/Ce/SBA-15 (OPA) was studied within the temperature range of 720-820 oC. The optimal reaction temperature was found at 800 oC with the minimum energy required of CH4 (25.09 kJ/mol) and CO2 (22.94 kJ/mol) obtained from Arrhenius plots. It was proven that 7Co/Ce/SBA-15 (OPA) at 800 oC was appreciably stable for 56 h time-on-stream (TOS). The highest catalytic performance was achieved over 7Co/Ce/SBA-15 (OPA) with 97.6 % of CO2 conversion and 96.3 % of CH4 conversion. In summary, 7Co/Ce/SBA-15 (OPA) was successfully synthesized and had been identified as a highly sustainable catalyst in DRM. The discovery of the combination between SBA-15 (OPA) that possessed highly ordered hexagonal structure as evidence in TEM with large surface area (524.74 m2/g) synthesized from waste material with Ce and Co metals provide an excellent catalytic activity and stability for DRM.