All the chemicals and reagents were of high purity grade (supplied by Scharlau, Spain) and used without any further purification. Nitrogen, oxygen and air were supplied by BOC Pakistan and further purified by specific filters (C.R.S.Inc.202268 & C.R.S.Inc.202223).

The crushed peanut shells were soaked in 50 weight % H₃PO₄ solution overnight at room temperature. The soaked sample was then loaded into a quartz tube and heated to 450˚C at a heating rate of 0.5˚C/min in tube furnace under nitrogen flow (40 mL/min) and then maintained at 450˚C for 60 min. The sample after cooling was washed in modified Soxhlet’s apparatus, and then dried. Finally, the sample was sieved through US standard sieve (80 and 100 Mesh).

0.5 M solution of ammonium hydroxide and 0.1 M solution of iron nitrate (cyclohexane/iron nitrate 100:0.25) were mixed in a 250 mL flask. Ammoniumhydroxide solution was added drop wise to iron nitrate solution while the resulting mixture was stirred vigorously. The mixture was then kept for 5 - 9 hours to allow for aging. Upon aging, the solution turned black indicating that iron oxide nanoparticles were formed. In the next step, 4.0 g of activated carbon was stirred with the solution of iron oxide nanoparticles in order to obtain 10 wt% iron oxide nanoparticles on activated carbon. The solution was filtered and the filter cake was dried at 70˚C overnight in an oven. Then it was calcined in muffle furnace by heating to 280˚C at a heating rate of 0.5˚C/min and then maintaining at the same temperature for 2 hours.

Catalytic activity of the catalyst was tested by carrying out the reaction in a three-necked batch reactor. 0.5 M aqueous solution of octanol (10 mL) and 100 mg catalyst was loaded into a reactor and sonicated at 60˚C in the presence of dry oxygen for 30 - 60 min. The reaction mixture was then analyzed by UV spectrophotometer (UV-1800, Shimadzu, Japan) by standard addition method, and GC (Clarus 580, PerkinElmer, USA) equipped with FID.

Iron oxide nanoparticles supported on activated carbon were characterized by SEM (JSM 5910, JEOL, Japan), XRD (X-ray diffractometer Rigaku D/Max-II, Cu tube, Japan), FTIR (Prestige 21 Shimadzu Japan in the range 500 - 4000 cm⁻¹), and surface area and pore size analyzer (Quantachrome Nova 2200e, USA).

Iron oxide nanoparticles (8 - 15 nm) were supported on activated carbon having particle size of 149 - 177 µm (U.S. Mesh). FT-IR spectra reveal that the surface functional groups of activated carbon are: O-H, N-H (3100 - 3500 cm⁻¹), C-H aromatic compound (3000 - 3100 cm⁻¹), C-H aliphatic compound (2800 - 3000 cm⁻¹), C=O and C-O (1640 - 1750 cm⁻¹). FT-IR of iron oxide nanoparticles supported on activated carbon shows characteristic peaks for aliphatic phosphate stretch at 1050 cm⁻¹ and 2300 cm⁻¹ and for hematite at 470 cm⁻¹ and 570 cm⁻¹ as shown in Figure 1. SEM images show a porous surface morphology of the activated carbon and also reflect the dispersion of iron oxide nanoparticles on the surface of activated carbon, as shown in Figure 2.

BET surface area of activated carbon is 1253.78 m²/g and pore volume is 0.71 cc/g while the surface area of iron oxide nanoparticles supported on activated carbon is 1235.67 m²/g and pore volume is 0.69 cc/g. The decrease in surface area results probably from the blockage of surface pores of activated carbon by iron oxide nano particles. XRD results of activated carbon, and iron oxide nanoparticles supported on activated carbon are shown in Figure 3. The XRD of activated carbon shows the amorphous morphology of the activated carbon while the intense reflections in the XRD of iron oxide on activated carbon show the presence of γ-hematite nanoparticles on the surface of activated carbon.

To assess the activity of the catalyst, liquid phase dehydrogenation/oxidation of octanol to octanal was carried out in a batch reactor in the presence of the catalyst under conditions as depicted in Scheme 1.

The results obtained for the reaction carried out under various conditions are presented in Table 1. The results show that the reaction with activated carbon as a catalyst was totally selective for the dehydration of octanol to octene with a very low % conversion. However, with Fe₂O₃/AC, the reaction was impressively selective for the oxidation of octanol to octanal. The discussion hereafter is only devoted to reactions catalyzed by Fe₂O₃/AC. Reaction conditions were optimized by varying one parameter at a time while others kept constant. The effect of the partial pressure of oxygen was studied at 60˚C and it was found that the rate of reaction raised linearly as the partial pressure of oxygen was increases, while the selectivity of the catalyst for octanal declined with an increase in the partial pressure of oxygen. Study of the effect of temperature revealed that there was an inverse relation between the reaction temperature and the selectivity of the catalyst for octanal. At constant temperature and pO₂, it was observed that as the reaction duration was extended, selectivity of the catalyst for octanal declined. A plot of lnC_o/C_tVS time where (C_o = initial concentration while C_t = final concentration) as shown in the Figure 4 has a sharp linearity with a regression value of 0.997, which suggests that the reaction is of first order.