Stabilization of Al2O3 with Al-O-P structure in HF atmosphere for dehydrofluorination reactions with unexpected catalyst lifetime

Stabilizing metastable active centers under harsh reaction conditions represents a significant challenge in heterogeneous catalysis. The F-Al-O species exhibits excellent catalytic activity for the gas-phase dehydrofluorination of potent greenhouse gas hydrofluorocarbons (HFCs) to produce hydrofluoroolefins (HFOs). However, this species is prone to transform into the F-Al-F configuration via excessive fluorination, subsequently leading to catalyst deactivation because of coke deposition. To address this issue, we present a viable strategy for stabilizing the metastable active centers. Al 2 O 3 doped with boron (B), phosphorus (P), and sulfur (S) was synthesized via the sol-gel method. Results demonstrate that in the dehydrofluorination of HFC-245fa, the phosphorus-doped Al 2 O 3 catalyst (P-Al 2 O 3 ) outperforms its boron- and sulfur-doped counterparts, achieving a conversion of 87% compared to 68% and 49%, respectively. The incorporation of P significantly alters the coordination environment of Al 3 + within the Al 2 O 3 lattice, forming O-Al-O-P bonding configurations. During the subsequent dehydrofluorination reaction, these structures undergo fluorination to yield HF-resistant F-Al-O-P species. This process effectively impedes the deep fluorination of Al 2 O 3 into AlF 3 , thereby stabilizing the metastable F-Al-O active centers. Furthermore, this anti-fluorination mechanism significantly suppresses catalyst coking and prevents pore structure collapse. In the dehydrofluorination of HFC-245fa to HFO-1234ze, the P-Al 2 O 3 catalyst achieved a high conversion of 87%, representing an approximately threefold enhancement over conventional Al 2 O 3 , and no significant deactivation trend was observed after 500 h of reaction. This work provides a fundamental understanding of stabilizing metastable active centers and paves a practical pathway for designing robust catalysts for reactions under corrosive atmospheres.