3D-Printed Fe/γ-Al2O3 Monoliths from MOF-Based Boehmite Inks for the Catalytic Hydroxylation of Phenol

The synthesis of dihydroxybenzenes (DHBZ), essential chemical reagents in numerous industrial processes, with a high degree of selectivity and yield from the hydroxylation of phenol is progressively attracting great interest in the catalysis field. Furthermore, the additive manufacturing of catalysts to produce 3D printed monoliths would provide additional benefits to enhance the DHBZ synthesis performance. Herein, 3D cellular Fe/gamma-Al2O3 monoliths with a total porosity of 88% and low density (0.43 g.cm(-3)) are printed by Robocasting from pseudoplastic Fe-metalorganic frameworks (Fe-MOF)-based aqueous boehmite inks to develop catalytic monoliths containing a Fe network of dispersed clusters (<= 5 mu m), nanoclusters (<50 nm), and nanoparticles (similar to 20 nm) into the porous ceramic skeleton. The hydroxylation of phenol in the presence of hydrogen peroxide is carried out at different reaction temperatures (65-85 degrees C) in a flow reactor filled with eight stacked 3D Fe/gamma-Al2O3 monoliths and with the following operating conditions: C-phenol,C-0 = 0.33 M, C-phe(nol,0)/C-H2O2,C-0 = 1:1 molar, W-R = 2.2 g, and space time (tau = W.Q(L)(-1)) = 0-147 g(cat).h.L-1. The scaffolds present a good mechanical resistance (similar to 1 MPa) to be employed in a catalytic reactor and do not show any cracks or damage after the chemical reaction. DHBZ selectivity (S-DHBZ) of 100% with a yield (Y-DHBZ) of 32% due to the presence of the Fe network in the monoliths is reported at 85 degrees C, which represents an improved synthesis performance as compared to that obtained by using the conventional Enichem process and the well-known titanium silicalite-1 catalysts (S-DHBZ = 99.1% and Y-DHBZ = 29.6% at 80 degrees C). This printing strategy allows manufacturing novel 3D structured catalysts for the synthesis of critical chemical compounds with higher reaction efficiencies.

Automated summary

The 3D printing of Fe/gamma-Al2O3 monoliths with Fe-MOF-based inks allows for the production of catalytic structures with highly dispersed Fe clusters, nanoclusters, and nanoparticles. By conducting the phenol hydroxylation reaction in a flow reactor using these printed scaffolds, a DHBZ selectivity of 100% and a yield of 32% were achieved, showcasing improved synthesis efficiency compared to conventional methods.