(Al1−xCrx)4B6O15 (0.08≤x≤0.14): Metal borates catalyze the dehydration of methanol into dimethyl ether

PKU-5 (Al 4 B 6 O 15 ) is potentially a solid acid catalyst, and it possesses an interesting open-framework composed of [AlO 6 ] and [B 2 O 5 ] groups. PKU-5 shows a high thermal stability, while no physical and chemical properties were investigated thus far, because of the difficulty in its synthesis. Cr-stabilized PKU-5 with the formula (Al 1− x Cr x ) 4 B 6 O 15 (0.08 ≤ x ≤ 0.14) can be easily prepared by annealing Cr-doped PKU-1 precursors. XRD and TEM experiments demonstrate Cr 3+ has been successively incorporated into the framework of PKU-5. NH 3 -TPD measurements indicate that the partial substitution of Al 3+ by Cr 3+ leads to a small change of acid sites in total amounts and distributions. Cr-PKU-5 shows a good catalytic activity for methanol dehydration from 300 to 450 °C. Other operation conditions, such as the Cr 3+ content, space velocity of methanol were also discussed in detail to evaluate its catalytic performance.