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The ability of Rh based catalysts to remove undesired tars from biomass-derived syngas was examined under realistic operating conditions. Experiments were performed in a fixed bed reactor at temperatures of 650-850 °C and atmospheric pressure using C 6 H 6 as a model tar compound. Benzene conversion exhibited a strong dependence on temperature and H 2 O concentration in the feed. Significantly better catalyst performance was observed upon addition of Ce to the catalyst, which increased Rh dispersion and stability. The concentration of C 6 H 6 in the feed had very little effect on catalyst performance. CO 2 , H 2 , and CO cofeeds had positive, neutral, and negative effects, respectively, on C 6 H 6 conversion. A representative biomass-derived syngas mixture of N 2 , H 2 , CO, CO 2 , H 2 O, and C 6 H 6 was tested on the Rh-Ce catalyst at 850 °C and 2 SLPM total flow rate, resulting in almost complete C 6 H 6 conversion to a near equilibrium product stream.

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Many biological, chemical, and thermal pathways have been investigated as potentially efficient processing methods to utilize biomass as a renewable feedstock. Pyrolysis of biomass has been investigated as a process to produce gas and liquid products by using, amongst others, fluidized-bed, rotary kiln, and plate-ablative reactors. [1,2] However, many pyrolysis reactors are hindered by char production, resulting from limited heat transfer rates to the reactor. As a result, reactors are difficult to scale up due to the large heat inputs required to maintain operation, causing lower pyrolysis oil yields.Heat transfer rates to feed particles should be sufficiently high to prohibit char formation within pyrolysis reactors. Previous research has demonstrated the volatilization of cellulose particles on the front face of a Rh-Ce/a-Al 2 O 3 catalyst bed.[3]High-speed photography was used to image 300 mm cellulose particles impacting the 700 8C catalyst, pyrolyzing to liquid intermediate compounds that were then volatilized and convected into the catalyst bed and further reacted to synthesis gas. High heat transfer rates to the particles (3.4 MW m À2) resulted in the complete conversion of cellulose particles without char formation.An ideal pyrolysis reactor should operate continuously, efficiently, and char-free to maximize the yield of pyrolysis. Graham et al. demonstrated an ultrafast pyrolysis process that converted cellulose to more than 80 wt % gases at temperatures between 750 and 900 8C on millisecond timescales.[4] Wei et al. examined the fast pyrolysis of different biomass feedstocks by using a free-fall reactor with a residence time < 2 s. [5] Particles (300-450 mm) pyrolyzed at 700-800 8C yielded up to 80 wt % gases and 20 wt % char. Similar to these pyrolysis processes, the reactor presented here operates at millisecond residence times and high temperatures (700-900 8C); however, it is able to select for larger hydrocarbon liquid products, rather than gas products. A fraction of the cellulose pyrolysis vapors (10-40 %, Table 1) are sacrificially oxidized to CO 2 and H 2 O to provide heat to the front face for pyrolysis allowing for autothermal and char-free operation.Reactions were carried out in a quartz reactor tube (internal diameter 19 mm) over a fixed catalyst bed (1 cm), as shown in Figure 1. Two types of supports were used: a cylindrical monolith [16 mm diameter, 10 mm long, 65 ppi (pores per linear inch) a-Al 2 O 3 , 5 wt% g-Al 2 O 3 washcoat] and spheres (1 cm bed, 1.3 mm diameter a-Al 2 O 3 ). Metals were impregnated onto the supports by using the incipient wetness technique, described previously.[6] Rh-Ce catalysts contained 2.5 wt % of each metal, Pt was applied to the support at 2.5 wt %. Mass flow controllers fed N 2 , O 2 , CH 4 , and H 2 into the reactor. Methane (0

in Wiley InterScience (www.interscience.wiley.com).The millisecond autothermal reforming of benzene, toluene, ethylbenzene, cumene, and styrene were independently studied over five noble metal-based catalysts: Pt, Rh, Rh/c-Al 2 O 3 , Rh-Ce, and Rh-Ce/c-Al 2 O 3 , as a function of carbon-to-oxygen feed ratio. The Rh-Ce/c-Al 2 O 3 catalyst exhibited the highest feedstock conversion as well as selectivities to both synthesis gas and hydrocarbon products (lowest selectivities to H 2 O and CO 2 ). Experimental results demonstrate a high stability of aromatic rings within the reactor system. Benzene and toluene seem to react primarily heterogeneously, producing only syngas and combustion products. Ethylbenzene and cumene behaved similarly, with higher conversions than benzene and toluene, and high product selectivity to styrene, likely due to homogeneous reactions involving their alkyl groups. Styrene exhibited low conversions over Rh-Ce/c-Al 2 O 3 , emphasizing the stability of styrene in the reactor system. V

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