Highly efficiency H2 production for real coal tar steam reforming over Ni-ca/H-Al catalyst: Effects of oxygen vacancy, CaO doping and synthesis methods.

Steam reforming of medium-low temperature coal tar (SRT) to produce H 2 is important for addressing the energy crisis and challenges of global climate change. However, current catalysts still suffer from low H 2 selectivity, low tar conversion and poor long-term stability due to the complex composition of real coal tar. Herein, a series of Ni-Ca/H-Al catalysts were prepared by different methods. The results showed that the acid pretreatment effectively removed the hydroxyl groups on the surface of γ-Al 2 O 3 to form oxygen vacancies (Ov), and the NiO was mainly anchored in the Ov. The cit-Ni-2Ca/H-Al catalyst prepared by citric acid-assisted impregnation exhibited the highest H 2 yield (152.74 mmol/g -tar), while CO 2 was only 22.11 mmol/g -tar. Characterization showed that the addition of CaO improved the dispersion of NiO and increased the Ov concentration. The increase in Ov weakened the Ni O bonds in NiO and facilitated the low-temperature reduction of NiO. The cit-Ni-2Ca/H-Al catalysts prepared by the citric acid-assisted impregnation method had better dispersion and strong basic sites compared with the impregnation and precipitation methods, leading to more active sites for CO 2 and H 2 O adsorption, and improving the carbon build-up resistance and reusability of the catalysts. Py-GC/MS results showed the cit-Ni-2Ca/H-Al had excellent tar deoxidation ability and effectively promoted the breakage of C C bonds in furans, benzene ring branches, and C O bonds in aliphatic hydrocarbons. The cit-Ni-2Ca/H-Al catalyst exhibited high tar conversion (90.96%) and H 2 yield (146.27 mmol/g -tar) without any treatment for at least 8 cycles. Interestingly, the H 2 yield reached 151.58 mmol/g -tar by the simple regeneration of cit-Ni-2Ca/H-Al. This study provides a theoretical basis for efficient steam reforming of real coal tar for H 2 production and catalyst preparation. [Display omitted] • The acid wash pretreatment increased the oxygen vacancies on the γ-Al 2 O 3 surface. • The oxygen vacancies provided defect sites for NiO anchoring. • CaO improved the dispersion and strong basic sites of the catalyst. • Cit-Ni-2Ca/H-Al showed high H 2 yield (152.74 mmol/g) and low CO yield (22.11 mmol/g). • Cit-Ni-2Ca/H-Al catalyst showed excellent reuse and regeneration performance. [ABSTRACT FROM AUTHOR]