Kinetic modelling of the liquid-phase hydrogenation of cinnamaldehyde on copper-based catalysts

ALBERTO J. MARCHI; JOSÉ F. PARIS; NICOLÁS M. BERTERO; CARLOS R. APESTEGUÍA

INDUSTRIAL & ENGINEERING CHEMICAL RESEARCH

ACS Publications

Año: 2007 vol. 46 p. 7657 - 7666

0888-5885

The liquid-phase hydrogenation of cinnamaldehyde (CAL) on copper-based catalysts was studied using pseudo-homogeneous and heterogeneous Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics. Three catalysts were employed: Cu/SiO2, prepared by incipient wetness impregnation, and Cu-Al and Cu-Zn-Al, obtained by coprecipitation. The pattern found for activity and selectivity to cinnamyl alcohol (COL) was: Cu-Zn-Al > Cu-Al > Cu/SiO2. The best fitting using LHHW models was obtained, in all the cases, by assuming total surface coverage. However, and in agreement with pseudo-homogeneous analysis, the best fitting for Cu/SiO2 and Cu-Al was achieved by considering that CAL is much more strongly adsorbed than products on metal copper sites to yield essentially hydrocinnamaldehyde (HCAL). In contrast, the best fitting for Cu-Zn-Al catalyst was obtained by considering that: 1) the adsorption strength values of CAL, HCAL, and COL on the catalyst surface are similar; 2) CAL is adsorbed on two different types of active sites; specifically CAL adsorbs on Cu0 to form HCAL and on Cu-Zn2+ interface sites to produce essentially COL. The modelling of catalytic data using LHHW kinetics and the estimated parameters allowed to interpreting the reasons for the higher COL formation rate observed on Cu-Zn-Al as compared to Cu/SiO2 and Cu-Al catalysts.2, prepared by incipient wetness impregnation, and Cu-Al and Cu-Zn-Al, obtained by coprecipitation. The pattern found for activity and selectivity to cinnamyl alcohol (COL) was: Cu-Zn-Al > Cu-Al > Cu/SiO2. The best fitting using LHHW models was obtained, in all the cases, by assuming total surface coverage. However, and in agreement with pseudo-homogeneous analysis, the best fitting for Cu/SiO2 and Cu-Al was achieved by considering that CAL is much more strongly adsorbed than products on metal copper sites to yield essentially hydrocinnamaldehyde (HCAL). In contrast, the best fitting for Cu-Zn-Al catalyst was obtained by considering that: 1) the adsorption strength values of CAL, HCAL, and COL on the catalyst surface are similar; 2) CAL is adsorbed on two different types of active sites; specifically CAL adsorbs on Cu0 to form HCAL and on Cu-Zn2+ interface sites to produce essentially COL. The modelling of catalytic data using LHHW kinetics and the estimated parameters allowed to interpreting the reasons for the higher COL formation rate observed on Cu-Zn-Al as compared to Cu/SiO2 and Cu-Al catalysts.