Oxidative ethanol steam reforming

Oxidative ethanol steam reforming (OESR), also called autothermal reforming of ethanol, takes place in the presence of oxygen in feed ... 

Aupretre, F., Descorme, C., Duprez, D., Casanave, D., and Uzio, D. Ethanol steam reforming over MgxNi1.xAl203 spinel oxide-supported Rh catalysts. Journal of Catalysis, 2005, 233 (2), 464. 

Ethanol steam reforming catalysts were developed by Men et al. [24]. Nickel, rhodium and ruthenium catalysts on different carrier materials such as alumina, silica, magnesia and zinc oxide were tested at a S/C ratio of 1.5 and WHSV 90 Lh g J in the temperature range 400-600 °C. All the monometallic catalysts were mainly selective for acetaldehyde and ethylene. Over the rhodium catalyst, a reaction temperature of 600 °C was required to achieve 80% hydrogen selectivity. 

Nickel-based catalysts on various carriers such as alumina, lanthana, magnesia and zinc oxide have been studied intensively for ethanol steam reforming [196]. 

Batista et al. performed ethanol steam reforming over cobalt/alumina and cobalt/ silica catalysts containing 8 and 18wt.% cobalt [201]. Even with a reaction temperature of400 °C, 70% conversion could be achieved. Methane was the main by-product, ethylene was only formed over samples containing 8 wt.% cobalt. Then a bed of an iron oxide/chromium oxide water-gas shift catalyst was switched behind the cobalt/ silica catalyst. The carbon monoxide was converted as expected, but also less methane was found in the product [202]. Even less carbon monoxide was formed when both catalysts were mixed. Sahoo et al. varied the cobalt content of the cobalt/alumina catalyst from 10 to 20 wt.%. The highest activity was determined for the sample containing 15 wt.% cobalt [203]. 

Cobalt/zinc oxide catalysts show low temperature activity for ethanol steam reforming even below 400 °C, along with low or no selectivity towards carbon monoxide, which has been reported by Uorca and coworkers [204,205]. However, residence time over the catalysts needs to be sufficiently low and the S/C ratio rather high to achieve this performance. 

Homs et al. reported that nickel supported on zinc oxide is not a favourable catalyst formulation for ethanol steam reforming, but the addition of nickel to a cobalt/zinc oxide catalyst promoted with sodium increased the catalytic activity [206]. At S/C 6.5 and only 300 °C reaction temperature, full ethanol conversion could be achieved without by-product formation, apart from methane. 

Urasaki et al. [56,57] demonstrated that Co and Ni catalysts supported on SrTiOs or LaAl203 were more stable during ethanol steam reforming than their counterpart supported on y-AlaOs or MgO, due to the inhibition of carbon deposition. On the contrary, Co/BaTiOs, with badly dispersed Co particles, presented a poor coke resistance. It was inferred that the lattice oxygen in perovskites played a positive role in the stability of the catalyst by inhibiting coke formation but only if the metal particle size is small enough to optimize the metal-support interface and then the transfer of oxygen to favor the oxidation of coke precursors. The addition of a small amount of a second metal, such as Fe and Rh on Co/SrTiOs promoted the ethanol conversion and the H2 yield [58]. 

H2 production from ethanol (as well as methanol) employs these methodologies either as such or after slight modifications, especially in the ATR process, wherein a separate combustion zone is usually not present (Scheme 3). A mixture of ethanol, steam and 02 with an appropriate ethanol steam 02 ratio directly enters on the catalyst bed to produce syngas at higher temperature, around 700 °C.18,22 The authors of this review believe that under the experimental conditions employed, both steam reforming and partial oxidation could occur on the same catalyst surface exchanging heats between them to produce H2 and carbon oxides. The amount of 02 may be different from what is required to achieve the thermally neutral operation. Consequently the reaction has been referred to as an oxidative steam reforming... 

Oxidative Steam Reforming (OSR) / Autothermal Reforming of Ethanol... 

Oxidative steam reforming/autothermal reforming of ethanol... 

Fig. 11 Free energy changes in the oxidative steam reforming/autothermal reforming of ethanol, acetaldehyde and methane.

Fig. 12 Thermodynamic equilibrium compositions on dry basis for the oxidative steam reforming of ethanol. All species are in gas phase. Initial concentrations of CO, CH4, CH3CHO are taken as zero in the calculation.

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