Pd-C Catalytic Thin Films Prepared by Magnetron Sputtering for the Decomposition of Formic Acid

Abstract

Formic acid is an advantageous liquid organic hydrogen carrier. It is relatively nontoxic and can be synthesized by the reaction of CO2 with sustainable hydrogen or by biomass decomposition. As an alternative to more widely studied powdery catalysts, supported Pd-C catalytic thin films with controlled nanostructure and compositions were newly prepared in this work by magnetron sputtering on structured supports and tested for the formic acid decomposition reaction. A two-magnetron configuration (carbon and tailored Pd-C targets) was used to achieve a reduction in Pd consumption and high catalyst surface roughness and dispersion by increasing the carbon content. Activity and durability tests were carried out for the gas phase formic acid decomposition reaction on SiC foam monoliths coated with the Pd-C films and the effects of column width, surface roughness and thermal pre-reduction time were investigated. Activity of 5.04 molH2·gPd−1·h−1 and 92% selectivity to the dehydrogenation reaction were achieved at 300 °C for the catalyst with a lower column width and higher carbon content and surface roughness. It was also found that deactivation occurs when Pd is sintered due to the elimination of carbon and/or the segregation and agglomeration of Pd upon cycling. Magnetron sputtering deposition appears as a promising and scalable route for the one-step preparation of Pd-C catalytic films by overcoming the different deposition characteristics of Pd and C with an appropriate experimental design.

Formic Acid Dehydrogenation over Ru- and Pd-Based Catalysts: Gas- vs. Liquid-Phase Reactions

“…In previous studies of the FAD reaction, Pd- and Ru-based catalysts were incapable of achieving complete formic acid conversion and 100% H 2 selectivity at once [ 23 , 39 , 58 ]. Arzac et al [ 23 ] prepared a Pd-C thin film supported on a SiC monolith, giving a conversion and selectivity of 80% and 88% at 350 °C, respectively. Selectivities higher than 90% were found at temperatures below 250 °C, with conversion values nearing 20% in dry conditions.…”

“…Liquid—aqueous-phase FAD would help to suppress dehydration reaction, and it has been studied extensively [ 17 , 18 , 19 , 20 , 21 ] although many of these works used homogeneous catalysts that limit the large-scale application of the process [ 22 ]. Regarding gas-phase FAD, it has also been studied [ 23 , 24 , 25 , 26 ], and it has been found that the addition of steam could shift the selectivity towards the dehydrogenation reaction [ 27 ]. Comparing both the liquid- and gas-phase reactions, it seems that the latter may be more attractive from an industrial point of view.…”

“…As for the active phase, metals such as Au, Ag, Pd, Pt, Ru, and Ir have been widely studied for the FAD reaction [ 19 , 28 , 32 , 33 , 34 , 35 ], with Pd being the preferred one due to its high stability and selectivity [ 23 ]. In fact, the current tendency to improve FAD performance consists of the application of bi- or tri-metallic Pd-based catalysts (as alloys, core–shell structures, etc.…”