ABSTRACT
All the catalysts were prepared using the coprecipitation procedure. Aqueous solutions of Fe(NO3)3•9H2O (0.5 M) (99%, Merck, Germany) and Mn(NO3)2•4H2O (0.5 M) (99.5%, Merck, Germany) with dierent molar ratios were premixed and the resulting solution heated to 70ºC in a round-bottomed ask tted with a condenser. Aqueous Na2CO3 (0.5 M) (99.8%, May & Baker, France) was added dropwise to the mixed nitrate solution, which was continuously stirred whilst the temperature was maintained isothermally in the range of 40-80°C. e nal pH achieved was varied between 6.3 and 10.3. is procedure took approximately 10 minutes to complete. e resulting precipitate was then left in this medium at the required pH and temperature used for the precipitation for times ranging from 0 to 5 hours. e precipitate was rst ltered and then washed several times with warm distilled water until no further Na+ was observed in the washings tested by am atomic absorption. e precipitate was then dried at 110°C for 16 hours to give a material denoted as the catalyst precursor which was subsequently calcined in static air in the furnace (650°C, 6 hours) to give the nal catalyst. For preparation of the supported catalysts, the same amount (20 wt%) of each support such as TiO2 (98%, May & Baker), SiO2 (98%, Merck), γ-Al2O3 (98%, Merck), MgO (98%, Merck), and ZSM-5 zeolite (99%, Aldrich, UK) has been added separately to the mixed solution of iron and manganese nitrates with nominal ratio of Fe/Mn=1/1. After the test of all these supported catalysts, it was found that Al2O3 is the best support than the others, so the Al2O3 loading of 5, 10, 15, 20, and 25 wt% based on the total catalyst weight, were used to obtain the best loading of Al2O3 support. e supported catalyst was then promoted with different promoters (Li, K, Rb, and Mg) by adding a small amount (1.5 wt%) of LiNO3 (99.5%, Prolabo, France), KNO3 (99%, Merck), RbCl (99%, Prolabo), and Mg(NO3)2⋅6H2O (99%, May & Baker) as separately to the suspension containing 50%Fe/50%Mn/5 wt.%Al2O3.
