Production of H₂-free CO by decomposition of formic acid over ZrO₂ catalysts

The decomposition of formic acid (HCOOH) over ZrO₂ catalysts synthesized by precipitation method was investigated and their catalytic activity based on unit mass of catalyst was compared by varying the calcination temperature in the 500–1000 °C range. The calcined ZrO₂ samples were characterized using temperature-programed desorption (TPD) of iso-propanol (IPA), H₂O, and HCOOH as well as X-ray diffraction (XRD), pyridine-adsorbed infrared spectroscopy (Py-IR) and N₂ sorption. The catalytic activity as a function of the calcination temperature of ZrO₂ showed a volcano-type curve with a maximum at 900 °C. The catalytic activity of ZrO₂ in the decomposition of HCOOH well correlated with Brönsted acid site density, and it was influenced by the crystalline phase of ZrO₂. Furthermore, the evolution of the Brönsted acid site density measured by Py-IR as a function of the calcination temperature was in good accordance with the desorption temperature determined by IPA- and HCOOH-TPD experiments. When H₂O vapor was added, the conversion of HCOOH slightly decreased, while the CO selectivity remained almost constant. However, when CO was supplied, the conversion of HCOOH decreased continuously, and the selectivity to H₂ gradually increased, indicating that the formation of zirconium suboxides with characteristics approaching those of metals was successful using CO as a reductant.