High-Throughput Continuous Flow Synthesis of Nickel Nanoparticles for the Catalytic Hydrodeoxygenation of Guaiacol

The translation of batch chemistries to high-throughput flow methods addresses scaling concerns associated with the implementation of colloidal nanoparticle (NP) catalysts for industrial processes. A literature procedure for the synthesis of Ni-NPs was adapted to a continuous millifluidic (mF) flow method, achieving yields >60%. Conversely, NPs prepared in a batch (B) reaction under conditions analogous to the continuous flow conditions gave only a 45% yield. Both mF- and B-Ni-NP catalysts were supported on SiO₂ and compared to a Ni/SiO₂ catalyst prepared by traditional incipient wetness (IW) impregnation for the hydrodeoxygenation (HDO) of guaiacol under ex situ catalytic fast pyrolysis conditions (350 °C, 0.5 MPa). Compared to the IW method, both colloidal NPs displayed increased morphological control and narrowed size distributions, and the NPs prepared by both methods showed similar size, shape, and crystallinity. The Ni-NP catalyst synthesized by the continuous flow method exhibited similar H-adsorption site densities, site-time yields, and selectivities toward deoxygenated products compared to the analogous batch-prepared catalyst, and it outperformed the IW catalyst with respect to higher selectivity to lower oxygen content products and a 31-fold decrease in deactivation rate. These results demonstrate the utility of synthesizing colloidal Ni-NP catalysts using flow methods that can produce >27 g/day of Ni-NPs (equivalent to >0.5 kg of 5 wt % Ni/SiO₂), while maintaining the catalytic properties displayed by the batch equivalent.