Influences of calcination temperature on the efficiency of CaO promotion over CaO modified Pt/γ-Al2O3 catalyst

The cyclohexane dehydrogenation on CaO modified Pt/γ-Al2O3 was investigated with the aim of understanding the influences of calcination temperature of CaO modified γ-Al2O3 support (Ca/Al) on the efficiency of CaO promotion. The results showed that the catalyst calcined at 600 °C exhibited the worst, while the one calcined at 800 °C showed the best catalytic performance during the variation of Ca/Al calcination temperature from 500 to 900 °C. The catalyst pretreated at 800 °C exhibited an excellent hydrogen productivity of up to 4.45 L/(gcat h) and high stability during 80 h continuous investigation of cyclohexane dehydrogenation in the absence of co-feed hydrogen at 300 °C and 8000 h−1 space velocity. That was attributed to weaker Pt–Al interaction and higher dispersed Pt, deriving from larger CaO particles. According to XRD spectra of model catalysts and CO2-TPD of Ca–Pt/Al catalysts, the efficiency of CaO promotion depended on the Ca–Al interaction strength and particle size instead of quantity of free CaO particles. The main calcium compound was free CaO in catalysts with low CaO content and low calcination temperature (below 800 °C). Complex CaO with high Ca–Al interaction strength and less CaO properties are formed in Ca900–Pt/Al catalyst.

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► The catalyst calcined at 800 °C exhibits the best catalytic performance.
► Initial activity, stability, Pt dispersion, Pt–Al interaction strength and CaO particle size present a sigmoidal curve tendency.
► The efficiency of CaO promotion effect depends on Ca–Al interaction strength and free CaO particle size.
► A complex with high Ca–Al interaction strength is formed at 900 °C in low CaO content catalysts.