Catalytic pyrolysis of glycerol into syngas over ceria-promoted Ni/α-Al2O3 catalyst

Highlights

Ceria promoted Ni/Al2O3 catalyst was employed for producing syngas from glycerol.

The rank of gaseous product yields in descending trend was H2 > CO > CO2 > CH4.

Activation energy were 26.91 (H2), 26.31 (CO), 24.71 (CO2) and 24.42 (CH4) kJ mol−1.

Reaction mechanism involves a single site associative adsorption of glycerol molecule.

The presence of an elongated whisker-type carbon was detected on the used catalyst.

Abstract

This paper reports on the catalytic pyrolysis of glycerol into syngas over a 3 wt%Ce-20 wt%Ni/77 wt% α-Al2O3 catalyst and at reaction temperatures of 973 K, 1023 K and 1073 K. NH3– and CO2-TPD analyses have revealed that the as-synthesized catalyst was net acidic with acid-to-basic site ratio of 1.24. This provides ideal conditions for chemisorption of glycerol. In addition, the BET specific surface area was 2.89 m2 g−1. The small surface area can be attributed to the thermally stable α-Al2O3 support. In addition, the average crystallite size was 40.22 nm. The catalytic glycerol pyrolysis produced gaseous products that were comprised of H2, CO, CO2 and CH4 only with H2:CO ratios that were consistently less than 2.0. This ratio is suitable for Fischer-Tropsch synthesis. The yields of CO2 and CH4 were several folds lower than the yields of H2 and CO, indicating that the latter were from primary reaction, viz. glycerol decomposition whilst the former were from secondary competing reactions. In addition, the activation energy obtained via Langmuir-Hinshelwood model was 25.34 kJ mol−1. Used catalyst characterization showed that the carbonaceous deposit was in the forms of whisker-type. This type of carbon deposit would not physically deactivate the catalyst.

Keywords

  • Alumina;
  • Ceria;
  • Glycerol;
  • Nickel;
  • Pyrolysis;
  • Syngas

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