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The increase of alumina calcination temperature from 800 °C to 1300 °C results in the transformation of γ-Al 2 O 3 to α-Al 2 O 3 phase accompanying a decrease of specific surface area and the amount of tetrahedral Al 3+ sites. Over Ru–Ba/alumina catalysts, an increase in alumina calcination temperature would broaden the size distribution of Ru particles, enlarge the metal-to-oxide ratio of Ru, decrease the amount of surface hydroxyl groups, as well as lower the temperature for N 2 desorption. As a result, the increase of alumina calcination temperature lessens the effect of hydrogen poisoning and decreases the activation energy for ammonia synthesis. The Ru–Ba/Al 2 O 3 catalyst with alumina calcined at 980 °C having both θ-Al 2 O 3 and α-Al 2 O 3 shows ammonia synthesis rate three times higher than that with alumina calcined at 800 °C having a γ-Al 2 O 3 phase.
Lin et al. (Tue,) studied this question.