Unveiling the role of mixing in oxygen vacancy formation and metal dispersion during co-precipitation synthesis of catalysts in microreactor

Abstract

Oxygen vacancy concentration and metal dispersion are critical in the performance of metal oxide-supported metal nanoparticle (NP) catalysts. Herein, we unveil the effect of mixing on the microstructure formation of catalysts during co-precipitation synthesis in a microreactor based on a single-phase flow. The two characteristics were separately studied using Ce0.9Y0.1O2 and Ni–Al2O3 systems, Raman spectroscopy, and TEM techniques. A quasi-linear dependence between the ratio of lattice defects to lattice oxygen ((Ov + Oh)/F2g) and segregation index Xs (i.e., (Ov + Oh)/F2g = −5.8Xs + 0.2) and a negative correlation between Ni dispersion and Xs were determined, suggesting that the high and uniform supersaturation environment induced by efficient micro-mixing was favorable for the formation of crystals with abundant vacancies and small sizes. The H2O-TPSR and C3H6-TPSR experimental results demonstrated that the high oxygen vacancy concentration and Ni dispersion were beneficial to activation of O–H, C–C, and C–H bonds, respectively. Moreover, the Ni dispersion ability of CYO-Re-930 with abundant oxygen vacancy obtained at Xs = 0.003 was superior to that of CYO-Re-23, resulting in the better n-dodecane steam reforming (SR) performance of Ni/CYO-Re-930 catalyst (85.5 molDodecane·molNi−1·h−1). This study highlights the role of mixing in the structural formation of doped ceria and supported nickel synthesized by co-precipitation at the microscale and provides a promising approach for the continuous synthesis of catalysts with tunable oxygen vacancy concentrations and metal dispersions.