3.2.1. Effect of calcination temperature for the raw carbide slag
The catalytic activities of the calcined carbide slag catalysts were compared with Raw CS and commercial CaO under the same reaction condition. As shown in Table 4, the raw carbide slag (Raw CS) and CS-400 gave FAME yields of 48.0% (Entry 1) and 13.0% (Entry 2), respectively, while CS-650 exhibited the higher FAME yield of 91.3% (Entry 3), indicating that the catalytic activities of the carbide slag-based catalysts significantly depended on the calcination temperature. Furthermore, the catalytic activity followed the trend of CS-650 > CS-800 > CS-950 > CS-1100. In association with the CO2-TPD results, this sequence was the same with that of basicity in the strong region (520–700 °C). In accordance to the opinion [42], the stronger basicity was favorable for activating the methanol to dissociate into adsorbed methoxide group and H. Therefore, it could be inferred that the strong basic sites derived from O2 − were probably responsible for the enhanced catalytic activity.