The activity of promoted and unpromoted skeletal copper catalysts for the oxidative dehydrogenation of ethanolamine to sodium glycinate in strong NaOH solutions has been studied using a modified stirred autoclave that allows the reactants to be brought to the reaction temperature of 160 °C separately prior to mixing. This enables the study of activity and kinetics without complication from partial reaction and catalyst deactivation at lower temperatures. First order plots based on the continuous measurement of hydrogen evolution are close to linear throughout reaction. Unpromoted catalysts show substantial deactivation in repeated experiments but this can be eliminated by pretreatment in NaOH alone at temperatures above that used for reaction. This lowers the initial activity but helps the stability with treatment at 200 °C in 9.7 M NaOH being particularly effective. Small amounts of Cr 2O3, deposited from sodium chromate included in the NaOH solution used to prepare the catalysts by leaching of a CuAl2 alloy, are a highly effective promoter. Catalysts containing 1-1.5 wt.% Cr 2O3, pretreated in 9.7 M at 200 °C, are several times as active as their unpromoted counterparts through the course of six successive reaction cycles. The promoted catalysts exhibit a much higher surface area, which correlates with the retention of aluminium in used catalysts, but the connection to the improved activity is complex.
- Chromia promotion
- Raney copper