The conventional Ni/АЬОз catalyst and Ni/BCC catalyst available for steam reforming were used to test tar reforming performance. As mentioned in section 7.1 and discussed in section

7.3, the deposited carbon may cause for deactivating catalysts due to covering activate site of catalysts. In this section, all experiments were performed under steam injection with s/c: 0.6 mol/mol. The added steam was expected to suppress the deposited carbon on activate surface of catalysts. In this section, the effect of steam addition on tar conversion, gas yields, and carbon conversion were investigated. The reactivity both of the Ni/BCC and Ni/АЬОз have been compared and discussed in detail.

In the activity tests, the formation of products were observed for 120 min, all calculated results of the gas yields and C_gas were the average of the specific results from various specific sampling times, which started at 20 min after feeding biomass and then in 20 min intervals.

As illustrated in Figure 12 (a), the gas yields are shown lowest for non-catalyst, while higher gas yields have achieved for the catalysts. The great improvement of product gas for the case of Ni/BCC catalyst should be given more attention. Most main gas components (CH4, CO, CO2, H2) were higher than those of Ni/AhO3 catalyst. Especially, in the case of the Ni/BCC catalyst, CO and H2 yield were 10.8 and 12.3 [mmol/ g-sample daf] higher than those of the Ni/АЬОз catalyst. These satisfactory results could be explained by a part of the deposited carbon on the Ni/BCC catalyst and Ni/ BCC char had been gasified in the presence of steam according to the reaction pathway as following reaction equations (Eqs. (7-4), (7-5), and (7-6)) in the Table 1.

Steam might also produce a larger active surface of Ni/BCC by steam gasification of deposited carbon on the surface of catalyst, which is also evidenced by BET data of used catalyst. After 1 h operation, total free surface of the Ni/АЬОз decreased from 104 to 32 m2/g due to reduction of nanopores by blockage of deposited carbon and catalyst particle growth. While, total free surface of Ni/BCC lightly reduced from 350 to 339 m2/g, this is due to characteristic porosity of brown coal char. The results indicate that steam plays a very important factor to regenerate activity of the new catalyst by steam gasification of deposited carbon on catalyst and to significantly enhance the quality of product gas of woody biomass gasification.

Biomass carbon balance is illustrated in Figure 12 (b). It was carried out in a similar way as described in section 7.3 The blank on the top of each bar can be considered as a percentage of the C_tar which was calculated by equation 3-5 in section 7.3.

It is different from the pyrolysis process, approximately 16.5% carbon in the fresh Ni/BCC catalyst was gasified in the presence of steam. Its percentage was defined by comparing between carbon in the fresh Ni/BCC catalyst and carbon in used Ni/BCC catalyst. In the presence of the Ni/BCC, biomass carbon conversion (C_gas) was calculated by subtraction between carbon of total product gas and conversion carbon of fresh Ni/BCC, which is mentioned on above. Using that method, we found that highest C_gas and lowest C_tar were achieved as 66 and 4.4% for Ni/BCC catalyst test, respectively, while the C_gas and C_tar obtained were only 59.9% and 7.4% for Ni/AbO3 catalyst test, respectively. Biomass tar conversion obtained was approximately 88.9% in Ni/BCC catalyst. The results indicate better catalyst activity for Ni/BCC. The detailed mechanism for this high activity is unclear at the present, however, it can be explained that some of the following characteristics of the Ni/BCC catalyst might be associated with this activity: well distribution of nickel particles due to carbon functional group in brown coal, high porosity of the catalyst, mineral component. In addition, Tomita et al. [32] reported that in the presence of steam, tar might be absorbed on catalyst and then be gasified without forming soot. Even if carbon was formed on the catalyst surface, it could be easily gasified. He also found that the carbon deposited over nickel was rapidly gasified with hydrogen at 873 K by reaction 7-11 in Table 1 [33]. This fact that can be observed both of CH4 and H2 yields are higher than that of the Ni/A2O3 catalyst.