Co-precipitation continuous synthesis of the Ni-Rh-Ce0.75Zr0.25O2-δ catalyst in the membrane dispersion microreactor system for n-dodecane steam reforming to hydrogen

Abstract

Precipitation at the micro-scale to produce nanoparticles with small particle size and uniform dispersion is feasible. A membrane dispersion microreactor (MR) - matching spiral tube system was used to synthesize highly dispersed (MR)-Ni-Rh-Ce0.75Zr0.25O2-δ and (MR)-Ni- Ce0.75Zr0.25O2-δ catalysts with active metal particle sizes of 4.3 and 4.6 nm. Rapid nucleation of the catalyst precursor was achieved in the microreactor and ordered growth occurred in the spiral tube. Characterization by TEM, pulse CO chemisorption, and Raman spectroscopy prove that the catalysts synthesized in the microreactor system possess more oxygen vacancies and uniformly supported active metal than those in the stirred tank (S). The apparent activation energies of the catalysts for n-dodecane steam reforming (SR) increase in the following order: (MR)-Ni-Rh-CZO (62 kJ/mol) < (S)-Ni-Rh-CZO (67 kJ/mol) < (MR)-Ni- CZO (77 kJ/mol) < (S)-Ni-CZO (84 kJ/mol). The initial hydrogen yields of (MR)-Ni-Rh-CZO and (S)-Ni-Rh-CZO are 88 and 59%, respectively, at T = 650 °C, WHSV = 12 h−1, and S/C = 4. TPSR experiments indicated that (MR)-Ni-CZO mostly contributed to the cleavage of C–C and C–H bonds. The carbon deposition in the first 12 h of n-dodecane SR is only 2.4 mg/(g-cat·mol-H2). For optimizing the continuous synthesis method, the initial hydrogen yield can be further improved to above 95% by increasing the mixing intensity, decreasing the ratio of the dispersed to continuous phase, and increasing the spiral tube length to synthesize better-dispersed catalysts.