Design and fabrication of integral carbon monoliths combining 3D printing and sol–gel polymerization: effects of the channel morphology on the CO-PROX reaction

Abstract

A new method to synthesize integral carbon monoliths with a controlled channel morphology has been developed in this work by combining 3D-printing technology and sol–gel polymerization. By this method, robust and consistent carbon monoliths were obtained with a perfect replica of the channel architecture at a microscale range. As a proof of concept, a carbon monolith with tortuous channels that split and join successively along the monolith length has been designed, fabricated and tested as a CuO/CeO₂ support for the preferential oxidation of CO in the presence of H₂ (CO-PrOx), which is a topic of ongoing research for H₂ purification in fuel cells. The behavior of this novel carbon monolith catalyst has been compared with that of a counterpart catalyst prepared with a conventional honeycomb design. Results shown that the wide macroporosity of the carbon network favors the anchoring and dispersion of the active phase both in the channel surface and the carbon network. The channel architecture affects the gas diffusion both through the channel and the carbon network and consequently, affects the active phase accessibility and activity. T₅₀ (the temperature to achieve 50% CO conversion) decreases by almost 13 °C at 240 mL min⁻¹ in the carbon monolith with tortuous channels (T₅₀ = 79.7 °C) compared to the honeycomb monolith (T₅₀ = 93.1 °C). The turbulent path created by the tortuous channels favours the active phase–gas contact and even the gas diffusion inside the macropores of the carbon skeleton improving the catalytic performance of the active phase compared to that by the conventional honeycomb design. Thus, this work demonstrates the potential of 3D printing to improve the catalytic supports currently available.