Faeza, Imtiaz (2002) ADSORPTION OF ALCOHOL VAPOURS ON YTTRIA STABILIZED ZIRCONIA CATALYSTS. Doctoral thesis, Quaid-i-Azam University, Islamabad.

[img] Text

Download (17kB)


Yttria stabilized zirconia powders were prepared with 3, 5, 8 and 10 mol% of added yttria. The structural analysis of these samples was carried out using X-Ray Diffraction, Particle Size Distribution, Nitrogen Adsorption, Mercury Porosimetric and Scanning Electron Microscopic techniques. The XRD studies indicated that the Z3 Y and Z5Y were tetragonal whereas Z8Y and ZIOY were found to be cubic in shape. Surface area was calculated using Nitrogen Adsorption Isotherms. It was found that with an increase in mole percent of Y 20 j in zirconia, there was an increase in surface area up to 5 mol% but after that it started decreasing. Mieroporosity or the powders was calculated by applying Dubinin-Radushkevich equation to the data obtained from nitrogen adsorption. D-R plots were found to be linear in the low relative pressure region and then there was an upward deviation at higher relative pressure in all the five systems. This deviation from the linearity shows a heterogeneous system of micropores. The deviation may also be due to the capillary condensation in transitional pores or multilayer formation on the walls of macropores. Pore size distribution in all the powders was studied using Mercury Porosimetric Technique. The irreversibility of hysteresis in Mercury Porograms indicated the presence of 'ink bottle' pores. The results obtained from SEM technique indicated that particles were round in shape. The particles were found to be of non-uniform size distribution. Adsorption of MeOH EtOH, PrOH and BuOH on pure and yttria stabilized zirconia was carried out between 273 to 303K. The isotherms obtained were of Type II. The surface area was calculated using Langmuir and BET adsorption isotherm equations and was found maximum for Z5Y powder. The isosteric heat of adsorption was calculated. Heat of adsorption, in general, seemed to be consistent with the earlier proposed idea of two adsorption processes occurring simultaneously, one with a small activation energy and the other with a large activation energy. Thermodynamic parameters such as change in free energy, entropy and enthalpy of adsorption were calculated using Virial isotherm. It was found that maximum adsorption had taken place on Z5Y sample. Most probably it was due to the strongest affinity of Z5Y for the alcohols among all the samples. IR spectroscopic studies were also carried out in the range 4000 to 400 cm -1 and the adsorption of alcohols was confirmed by the results obtained. Water vapour adsorption on zirconia was also studied. The isotherm obtained was of Type V, a characteristic of weak gas-solid interactions. The value of surface area obtained from the water vapor adsorption was much lower than that obtained from the nitrogen adsorption.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: alcohol vapours, yttria stabilized zirconia catalysts, zirconia, yttria, 'ink bottle' pores
Subjects: Q Science > QD Chemistry
Depositing User: Muhammad Khan Khan
Date Deposited: 29 Sep 2016 10:36
Last Modified: 29 Sep 2016 10:36

Actions (login required)

View Item View Item