Characterization of Active Species in Cu-Beta Zeolite by Temperature-Programmed Reduction Mass Spectrometry (TPR-MS)

The number and type of copper species present in an under-exchanged Cu-Beta zeolite catalyst were characterized using temperature-programmed reduction mass spectrometry (TPR-MS). Both H₂ consumption and H₂O evolution were tracked, yielding additional insights into the nature of Cu species. Prior to the TPR-MS tests, catalyst samples were subjected to various high- temperature aging treatments in the presence of O₂ in He, in order to assist with interrogating and resolving different types of sites. Absence of reducible species in the precursor material was confirmed by subjecting the H-form of the same zeolite to the TPR. Upon aging at temperatures below 700 °C, the TPR pattern showed several distinct peaks of different intensities. Aging at 800 °C led to shifting and broadening of these H₂ consumption peaks, as well as to some reduction of the integral amount of the reducible sites. The 900 °C exposure resulted in a drastic change of the TPR pattern, with several new well-resolved H₂ consumption peaks, indicative of drastic changes in the catalyst structure. The integral amount of H₂ consumed quantitatively matched the amount of Cu species present in the catalyst, assuming the \( {\text{Cu}}^{ 2+ } \to {\text{Cu}}^{0} \) stoichiometry. The combination of experimental findings in this work lends support to a hypothesis that different TPR peaks are indicative of different types of sites rather than of step-wise reduction of copper species.