|
چکیده
|
Design of nanocatalysts with promoted anti-coke ability, high catalytic activity and stable performance during oxidative conversion of CH4/CO2 mixture to syngas was the purpose of this study. First, NiAl2O4, WNiAl2O4 and CoWNiAl2O4 nanocatalysts were fabricated using sol-gel technique. Then, plasma treatment was utilized for enhancement of CoWNiAl2O4. The fresh samples were characterized by XRD, FESEM, EDX, BET, TEM and FTIR analyses. Through the 48 h time on stream performance, methane conversion was dropped by 13% and coke deposition of 17.3% occurred during the stability test of NiAl2O4. Addition of tungsten into NiAl2O4, due to its ability in upgrading the rate of coke gasification, caused quite stable performance. In contrast, lower catalytic activity was found for WNiAl2O4 as a result of active sites coverage. It was made an effort to compensate the reduction of catalytic activity by cobalt addition. Smaller particle size and uniform dispersion were achieved for cobalt promoted nanocatalysts. Therefore, catalytic activity was ascended. However, for sol-gel prepared CoWNiAl2O4 high efficiency was found, but higher amount of deposited coke and deactivation were detected. The novel synthesis method i.e. hybrid sol-gel plasma alongside the cobalt and tungsten promoters caused a well-designed nanocatalyst. Promoted dispersion of active phases, finer particle size, stronger metal-support interaction and high surface area were achieved for plasma-enhanced sol-gel fabricated CoWNiAl2O4. Due to these tremendous properties, XCH4= 92% was obtained for this sample at 850 ◦C. A well-maintained structure and excellent dispersion were gained after 48 h TOS, as evidenced by FESEM and EDX images of used nanocatalysts.
|