Hydrogen is an important feedstock for the production of fertilizers, clean-burning transportation fuels, and chemicals.  Hydrogen also holds great promise as a fuel for high efficiency fuel cells and its production from renewable feedstocks could significantly reduce our nation's dependence on foreign energy sources and fossil fuels.  A promising, near-term renewable source for hydrogen is ethanol derived from biomass including energy plants, waste materials from agro-industries, forestry residue materials, or the organic fractions of municipal solid waste. Presently available catalysts do not appear to be sufficiently effective for commercial use [1].

Research described in this paper investigated the use of ZnO and ZnO/Al₂O₃ supported catalysts for the Steam Reforming of Ethanol (SRE). Metals including Pt, Rh, Pd and Ag were added to the supports using a dry impregnation method, and selected properties were listed in Table 1. The SRE experiments were carried out at 723K in a fixed bed quartz reactor with a molar ratio of ethanol to water 1:4. Reaction rates listed in Table 1 were those measured after 30 minutes on stream. Hydrogen and CH₃CHO formation rates were similar for the ZnO supported catalysts, except for Pt/ZnO. A significant amount of CH₄ produced by the Pt/ZnO catalyst suggests that CH₃CHO decomposed to CH₄ over this material. Surface areas for the ZnO supported catalysts were 20 m²/g.  In an effort to increase the surface area and perhaps improve the metal dispersion, we prepared a series of catalysts using supports where ZnO was dispersed onto g-Al₂O₃. The ZnO loading (20 wt%) corresponded to monolayer surface coverage and the surface areas were typically 130 m²/g. While rates and selectivities for the ZnO and ZnO/Al₂O₃ supports were similar, H₂ formation selectivities for the ZnO/Al₂O₃ supported catalysts were better than those for the ZnO supported catalysts suggesting differences in their surface chemistries. Surface chemical and structural properties for the catalysts were characterized using infrared spectroscopy and transmission electron microscopy.  Differences in the densities of surface acid and base sites appeared to account for differences in selectivity.  These and other results will be presented in this paper.

Table 1. Catalytic conversions and reaction rates at 723K after 30 minutes on stream.

Sample	Metal	Ethanol	Formation Rate µmol/(s∙g)
	Loading /%	Conversion /%	H2	CH3CHO	C2H4	CH4	Acetone
ZnO	-	52	56	36	9	0	5
Pt/ZnO	1	94	135	61	1	12	6
Rh/ZnO	2	51	81	60	14	1	3
Pd/ZnO	2	41	69	68	16	0	4
Ag/Al2O3	2	100	0	2	169	0	0
ZnO/Al2O3	-	54	60	45	5	0	2
Pd/ZnO/Al2O3	2	44	82	48	3	0	3
Ag/ZnO/Al2O3	2	40	79	52	4	0	3

Corresponding author: Levi T. Thompson , ltt@umich.edu

References

[1] Agus H., Sandun F., Naveen M., Sushil A., Energy & Fuels 2098, 19 (2005).