Nickel-based catalysts for steam reforming of naphthalene utilizing gasification slag from municipal solid waste as a support

Abstract

Nickel-based catalysts were synthesized using gasification slag as an abundant and inexpensive material with high mechanical strength. The synthesis procedure comprised of etching of gasification slag with hydrofluoric acid, aluminum hydroxide addition, impregnation with Ni and calcination. The naphthalene reforming activity was tested at 850 °C and 24,000 h−1 gas hourly space velocity in the presence of 50 ppmv H2S and 300 ppmv HCl in gas. The presence of aluminum hydroxide and an oxidizing environment during the calcination process were essential for preparation of active catalysts. The addition of 30% of aluminum hydroxide to gasification slag improved the dispersion of Ni oxide and increased the Brunauer–Emmett–Teller (BET) specific surface area determined by N2 adsorption at −196 °C from 4.5 to 15.0 m2 g−1 as compared to the catalyst without aluminum hydroxide. This resulted in the increased naphthalene conversion from 35 to 86%. The activity of Ni in synthesized slag catalyst was approximately 3.2 times higher than in commercial catalyst due to the deposition of Ni on the outer surface of catalyst particles. The deposited Al and Ni species were firmly attached to the slag particles during calcination at 500–1000 °C. While high calcination temperature was beneficial for high mechanical strength of catalyst, the procedure should be conducted under oxidizing environment. When calcination was carried out in N2 environment at 1000 °C, the sintering of catalyst particles and encapsulation of Ni occurred, which drastically decreased the BET specific surface area to 0.4 m2 g−1 and naphthalene conversion to 30%. These negative effects could be prevented when air was used during calcination, which facilitated earlier crystallization and inhibited excessive sintering of catalyst, thus, maintaining the high catalytic activity.