Selectivity engineering in the synthesis of value added chemicals: oxidation of 1-octanol to 1-octanal over nano-fibrous Ag–OMS-2 catalysts

Abstract

Oxidation of 1-octanol to 1-octanal is commercially very attractive, since the product is used extensively in the fragrance industry. Among the various methods, selective air oxidation with a suitable heterogeneous catalyst will be green and clean. In this work, novel cryptomelane type octahedral molecular sieve type 2 (Ag–OMS-2) catalysts, with Ag loading from 5 to 15%, w/w, were synthesized and evaluated in air oxidation of 1-octanol in a fixed bed vapour phase reactor. All catalysts were fully characterized to understand the activity and selectivity. The conversion increased with Ag loading but the selectivity was the highest for 10% Ag–OMS-2. A systematic study was conducted to ascertain the effects of various parameters. Use of toluene as a diluant leads to better conversion and selectivity. The optimized conditions are: catalyst mass/molar flow rate of 1-octanol (W/F_A0)- 20 g h/mol, 523 K, toluene to 1-octanol molar ratio- 4:1, weight hourly space velocity (WHSV)- 16.74 h−1, air flow rate- 6 L/h, air pressure- 101.3 kPa. It follows the Mars-van Krevelen mechanism and is intrinsically kinetically controlled. The activation energy is 14.39 kcal/mol using 10%, w/w Ag–OMS-2. It provides a better green process than those reported so far.