Enhanced selectivity and stability of Pt-Ge/Al2O3 catalysts by Ca promotion in propane dehydrogenation

[Display omitted] •Calcium increases Pt-Ge alloy extent by enhancing Ge reducibility.•Calcium significantly enhances catalyst stability and propylene selectivity.•Calcium selectively suppresses strong acid sites.•Calcium-promoted catalyst is less active for coke deactivation, (ψd).•Steady state activity is increased since Ca decreases ψd more than ψr. The promoting effect of Ca on the catalytic performance of Pt0.5-Ge1.5/Al2O3 during propane dehydrogenation (PDH) reaction was studied using experimental methods and kinetic modeling. Different characterization techniques including H2-TPR, NH3-TPD, C3H6-TPD, XPS, BET, CO-chemisorption, CO-DRIFT, and TGA were used to unravel the properties of catalysts. Enhanced propylene selectivity (98.5% Vs 96.4% @ 600 °C and 24 h TOS) and catalyst stability were achieved due to the decrease of acid centers of Al2O3 along with an increase of the degree of alloy formation upon addition of Ca. The experimental data of propane conversion vs. time were successfully fitted with the Deactivation Model with Residual Activity (DMRA), allowing for the calculation of the intrinsic deactivation kinetic parameters for both catalysts. For the Ca-promoted catalyst, a deactivation function of 0.05 h−1 along with a residual activity of 0.82 at 600 °C were obtained. Whereas, for the non-promoted sample, these values were 0.22 h−1 and 0.63, respectively. The activation energy of the PDH reaction for the Pt0.5-Ge1.5/Al2O3-CaO catalyst was slightly higher than that of the unmodified one (74.8 kJ/mol vs. 66.4 kJ/mol) due to the enhanced reduction of the GeOx species on this sample, which enhanced the formation of a Pt-Ge alloy, decreasing the initial activity of the catalyst. However, the higher resistance against the deactivation by coke of the promoted catalyst was invoked to explain the better performance of this catalyst in terms both of activity and selectivity at steady state conditions.