Both catalysts showed high conversion at atmospheric pressure
whereas the conversion drastically decreased at high pressure.
Fig. 9 shows that there is a significant amount of carbon
deposits formed on the Ni catalysts supported on Al2O3,
particularly under elevated pressures [11,12]. The use of Y
zeolite can reduce the carbon deposits significantly, but this
reduction becomes insignificant at elevated pressures. The
SEM photos shown in Fig. 10 reveal that filamental carbon
deposits (also called carbon nano-tubes) are formed on the
surfaces of Ni catalysts [11,12]. Higher carbon formation at
high pressure was observed as filamental carbon compared to at
atmospheric pressure.