Deactivation and Regeneration of Mn-Promoted Sulfated Zirconia Alkane Isomerization Catalysts: An In-Situ Spectroscopic Study

Mn-promoted sulfated zirconia (0.5 or 2 wt% Mn) was investigated during activation (in inert or oxidizing atmosphere at 703–773 K), during n-butane isomerization (323–333 K, 1 kPa n-butane) and during regeneration (see activation conditions) using in situ UV–vis–NIR, diffuse reflectance IR, and X-ray absorption spectroscopies. While the activation atmosphere did not influence the degree of hydration and the state of the sulfate, manganese—which was always present as a mixture of Mn2+ and higher oxidation states—was slightly reduced in the absence of oxygen. Catalytic data did not give a clear picture as to whether activation in oxygen-containing atmosphere is advantageous or not. The catalysts deactivated within hours, but complete recovery in O2 was possible. Heating of a deactivated catalyst in N2 produced an inactive material and unsaturated compounds on the surface.