Sulfate ion induced formation of unsaturated coordination of AlF3 nanocluster catalyst confined in carbon framework for catalytic dehydrofluorination

The gas-phase catalytic dehydrofluorination of hydrofluorocarbons (HFCs) to produce hydrofluoroolefins is an important strategy for the resource utilization of HFCs. AlF 3 is the most suitable and efficient catalyst for dehydrofluorination of HFCs. However, sintering and preservation of coordinatively unsaturated aluminum centers pose significant challenges for AlF 3 catalysts. Herein, we prepared carbon-confined AlF 3 nanocluster catalysts with aluminum fumarate metal organic frameworks (AlFu-MOF) as the precursors, followed by carbonization and fluorination treatments. During catalyst preparation, anion ligand in the aluminum salt plays a major role in the formation of coordinatively unsaturated Al centers. Compared with Al(NO 3 ) 3 ·9H 2 O and AlCl 3 ·6H 2 O, AlFu-MOF (named AlFu-S) prepared with Al 2 (SO 4 ) 3 ·18H 2 O exhibits a higher concentration of Al-OH species. Additionally, the residual SO 4 2- ions can indeed retard the crystallization of AlF 3 at elevated temperatures. Hence, the decomposition of Al-OH groups and the presence of residual SO 4 2- ions in AlFu-S contribute together to the abundance of unsaturated coordinated Al centers in the finally carbon-confined AlF 3 nanocluster catalyst (named AlFu-S-550-F). Also, the confinement effect of the carbon material formed by the carbonization of AlFu-S effectively prevent AlF 3 nanocluster from sintering and phase transition, hence, in the dehydrofluorination of HFC-134a, AlFu-S-550-F demonstrates excellent stability compared to AlF 3 catalysts prepared by precipitation methods. In summary, this study provides a strategy for the preservation of coordinatively unsaturated aluminum centers in AlF 3 catalysts due to sintering and crystal structure transformation. Furthermore, the methodology proposed in this work is also applicable to the preparation of other coordinatively unsaturated metal catalysts.