The most accepted structure of solid acid consists of a flexible carbon-based frame­work with highly dispersed polycyclic aromatic hydrocarbons containing sulfonic acid groups (Shu et al. 2010). Figure 15.6 represents the proposed schematic structure of the sulfonated carbon materials. Every sulfur atom presents in the catalyst exists as — SO3H, the sulfur content obtained from the analysis was used for calculating the sulfonic acid density (Ezebor et al. 2014) while SO3H + COOH and SO3H + COOH + OH densities were calculated from ion exchange (Kitano et al. 2009). Figure 15.7 shows the amorphous carbon bearing SO3 H groups as an insoluble Bronsted acid available for various acid-catalyzed reactions (Nakajima and Hara 2012).

The large amounts of SO3H group are present in the polycyclic aromatic groups constituting the carbon sheets of aromatic carbon. The strong hydrogen bonding to SO3H groups results in strong acidity due to mutual electron-withdrawal and creat­ing the reason behind their higher catalytic activity (Hara 2010). Figure 15.8 shows the sulfonic acid group SO3H groups bearing amorphous carbon (Nakajima et al.

2008) . Hydrophobicity that prevented the hydration of -OH species, its high acid site density (-OH, Bronsted acid sites) hydrophilic functional groups (-SO3H) that gave improved accessibility of methanol to the triglyceride and FFAs, and large pores that provided more acid sites for the reactants are the factors that increase the high catalytic activity and stability of the activated carbon catalyst (Shu et al. 2010).

Sulfonic acid group (SO3H)-bearing amorphous carbon well regarded as carbon- based solid acid catalysts. SO3 H-bearing carbon particles with large surface area inhibit intramolecular Friedel-Crafts alkylation, thus shows greater catalytic activ­ity that are revealed from structural and reaction analyses (Nakajima et al. 2008). The hydrolysis of p-1, 4 glycosidic bonds in both cellobiose and crystalline cellu­lose can be catalyzed by carbon-based solid acid catalyst. The large adsorption capacity for hydrophilic reactants and the adsorption ability of p-1, 4 glucan is responsible for the high catalytic performance of the carbon catalyst, which is not adsorbed to other solid acids (Suganuma et al. 2010).

15.2 Conclusions

Activated carbons were prepared from huge variety of cellulosic resources including agricultural wastes, municipal wastes, plants residues, and non-edible oil cakes wastes considering that biomass is renewable, abundant, and low cost, either using chemical activating agent or physical agents. The effect of parameters such as activation temperature, and impregnation ratio on pore structure and surface chem­istry of resulting carbons were also studied. By nitrogen adsorption the pore struc­ture of the activated carbon was studied, however functional group analyzed by FT-IR. The surface areas of the activated carbons were strongly affected by the carbonization temperature and concentration of the activation reagent. The obtained activated carbons mainly have microporous characteristics. Consequently, obtained activated carbons from the agricultural or industrial waste biomass can be utilized for the preparation of further sulfonated activated catalyst; however the catalytic properties depend upon the nature of attached molecule/group (acidic or basic), with the possibility to be utilized as heterogeneous catalysts in different chemical reactions. However, further works on economic study, improvement of catalytic stability, and mechanical strength should be conducted.