Vacuum-assisted continuous flow electroless plating approach for high performance Pd membrane deposition on ceramic hollow fiber lumen

Pd-based membranes have wide applications in H-2-related fields given their excellent selectivity in H-2 separation. Despite their unique advantages, the fabrication of continuous and dense Pd membrane layer in the lumen side of the hollow fibers remains a great challenge. Herein, a vacuum-assisted continuous flow electroless plating (VCFELP) approach was developed to deposit a 4 mu m-thick compact Pd membrane layer on the lumen (i.e., inner surface) of YSZ-Al2O3 composite hollow fiber with outer and inner diameter of 1.5 and 1.0 mm, respectively. The Pd membrane displayed hydrogen flux of ~0.075 mol m(-2) s(-1) at 773 K and the nitrogen was undetectable through bubble flow meter and gas chromatograph. Furthermore, the stability and durability of the Pd membrane were significantly improved by the VCFELP approach with the aid of vacuum and continuous flow system. The outstanding membrane stability was verified by the 240-h long-term operation, with up to 24 cycles of H-2-N-2 gas exchange tests, 40 thermal cycle tests (from high to low temperature) and 20 pressure cycle tests. Furthermore, the Pd membrane showed sufficient stability and excellent reaction performance during the 120-h reaction run in the one-step oxidation of benzene to phenol using hydrogen and oxygen as co-reactants, achieving the benzene conversion and phenol selectivity of 23.5% and 91.6%, respectively.