Open AccessSurface and Catalytic Properties of NiO and Fe2O3 Solids
Author(s) -
A. Abd. El-Aal,
A.M. Ghozza,
G.A. El-Shobaky
Publication year - 1997
Publication title -
adsorption science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.682
H-Index - 36
eISSN - 2048-4038
pISSN - 0263-6174
DOI - 10.1177/026361749701500805
Subject(s) - non blocking i/o , calcination , catalysis , chemistry , sintering , bet theory , adsorption , activation energy , atmospheric temperature range , stoichiometry , specific surface area , crystallization , analytical chemistry (journal) , inorganic chemistry , chemical engineering , mineralogy , chromatography , organic chemistry , thermodynamics , physics , engineering
The surface characteristics, viz., the specific surface area S BET , the total pore volume V p and the mean pore radius r̄, of NiO and Fe 2 O 3 were determined from N 2 adsorption isotherms conducted at −196°C for the different adsorbents preheated in air at temperatures in the range 300–800°C. The catalytic activities exhibited in CO oxidation by O 2 on the various solids were investigated at temperatures varying between 150°C and 400°C. The effect of heating the NiO and Fe 2 O 3 solids in CO and O 2 atmospheres at 175–275°C on their catalytic activities was also studied. The results showed that increasing the calcination temperature in the range 300–800°C resulted in a progressive decrease in the S BET value of NiO and Fe 2 O 3 . The computed values of the apparent activation energy for the sintering of the oxides were 71 and 92 kJ/mol, respectively. The sintering of NiO and Fe 2 O 3 took place mainly via a particle adhesion mechanism. The catalytic activity of NiO decreased progressively on increasing its calcination temperature from 300°C to 800°C, due to a decrease in its S BET value and the progressive removal of excess O 2 which was present as non-stoichiometric NiO. This treatment also decreased the catalytic activity of Fe 2 O 3 . The decrease was, however, more pronounced when the temperature increased from 300°C to 400°C which was a result of the crystallization of the ferric oxide into the α-Fe 2 O 3 phase. An increase in the calcination temperature for both oxides from 300°C to 800°C did not modify the mechanism of oxidation of CO by O 2 over the various solids but rather changed the concentration of catalytically active sites. Heating NiO and Fe 2 O 3 in CO and O 2 atmospheres at 175–275°C modified their catalytic activities, with Fe 2 O 3 being influenced to a greater extent than NiO.