Resilient Ni and Ni–Ru catalysts for daily start-up and shutdown methane steam reforming via urea-assisted deposition precipitation

In this study, we synthesized monometallic Ni and bimetallic Ni–Ru catalysts on Mg(Al)O mixed oxides using wet impregnation (WI) and urea-assisted deposition-precipitation (DPU) and evaluated them under daily start-up and shutdown (DSS) conditions in steam reforming of methane (SMR). Although all Ni catalysts featured optimally sized Ni nanoparticles (<6 nm), and therefore high activity, their stability depended strongly on the preparation route. The DPU-prepared Ni catalyst remained active for about 13 h (3 cycles), whereas the WI analogue deactivated within only 2 h. Introducing Ru markedly enhanced stability: all Ni–Ru catalysts stayed active for up to 24 h on stream and completed four DSS cycles, with DPU-derived samples performing best (the catalyst prepared by sequential impregnation showed 90% conversion and 3.7 mol H2 h−1 gcat−1 of H2 productivity). High-pH DPU treatment partially reconstructs the hydrotalcite phase, increasing surface area and porosity and improving metal reducibility, thereby enhancing their activity and stability. Overall, the Ni–Ru catalyst prepared via sequential DPU was the most active and stable. This work demonstrates that combining optimally sized metal nanoparticles with synthesis routes that promote high reducibility produces exceptionally robust SMR catalysts under the demanding conditions of DSS cycling.