Influence of metakaolinization temperature on the structure and activity of metakaolin supported Ni catalyst in dry methane reforming

Kaolin was transformed into metakaolin via thermal treatment and explored as Ni catalyst support for dry methane reforming (DMR). The metakaolinization protocol was carried out at three different temperatures (700, 800 and 900 degrees C) followed by incorporation of Ni precursor. The synthesized metakaolin nickel catalysts (Ni-MK@T) were characterized comprehensively with respect to the site, phase, adsorption and reducibility. The Fourier transformed infrared spectroscopy (FTIR) results showed that there was progressive combined dehydroxylation and dealumination (Al-OH) as the metakaolinization temperature (MKT) increases leading to the loss of basic sites. According to the x-ray diffraction patterns, kaolin transformed from highly crystalline to essentially amorphous structure after the metakaolinization process. As the MKT increases from 700 to 900 degrees C, the NiO particle sizes reduced from 13.9 to 9.3 nm, demonstrating that the extent of amorphization was very significant on Ni-MK@900 by restraining the agglomeration of NiO particles which was promoted by an increase in surface area. Temperature programmed reduction results showed that Ni-MK@800 achieved the highest H-2 reducibility leading to the highest CH4 conversion. The large NiO particle size in Ni-MK@700 and the high metal support interaction due to the very small NiO particle size in Ni-MK@900 resulted in lower reduced metal surface required for the DMR reaction. However, the CO2 conversion was higher over Ni-MK@700 since higher MKT leads to higher loss of basic sites due to Al-OH removal. The H-2/CO ratio over the catalysts followed Ni-MK@900 > Ni-MK@800 > > Ni-MK@700 due to the disparity between the CH4 and CO2 conversions arising from the metakaolinization process.