Metal doped carbon aerogels

Table 10.3 Textural Characteristics of Steam-Activated Metal-Doped Carbon Aerogels and the Blank NC-S ...

To date, metal-doped carbon aerogels and xerogels have been used as catalysts in different reaction types, which can be grouped into environmental and fuel cell applications, C=C double-bond hydrogenation, skeletal isomerization, hydrodechlorination, and other reactions, including synthesis of methyl... 

These authors used the term metal-doped carbon aerogels both in the title and throughout the text, although they were not in fact carbon aerogels because the organic aerogels were not carbonized, with the exception of that with Mn. The model compound chosen for the study was sodium j)tira-chlorobenzoate (pCBA). 

Sanchez-Polo M, Rivera-Utrilla J, Mendez-Diaz J, Lopez-Penalver J (2008) Metal - doped carbon aerogels new materials for water treatments. Ind Eng Chem Res 47 6001-6005. 

Sanchez-Polo M, Rivera-Utrilla J, von Gunten U (2(X)6) Metal-doped carbon aerogels as catalysts during ozonation processes in aqueous solutions. Water Res 40 3375-3384... 

Ce- and Zr-doped carbon aerogels were obtained by dissolving their nitrates in an R/F mixture at different pHs [39,40] and carbonized at 1323 K. Introdnction of the metal salts produced changes in the initial pH and therefore in the chemistry of the process. Some of the textural characteristics of these samples are compiled in Table 10.2. Their surface area ranged from 87 to 800 m /g, the micropore volume from 0.03 to 0.20 cm /g, and the micropore size from 0.65 to 0.90 nm... 

In other Pt-doped monolithic carbon aerogels, prepared by adding the Pt pre-cnrsor to the initial R/F mixture [41], the Pt particle size determined by H2 chemisorption was mnch higher than that determined by high-resolution transmission electron microscopy (HRTEM). This indicates that some Pt particles were encapsnlated by the carbon matrix and were consequently inaccessible to H2. This can be the main problem of this preparation method when the metal-doped carbon gel is to be used as catalyst, because part of the metal will not be accessible to the reactant molecules. 

Using the same method, Cotet and co-workers [54] prepared high-content Ee-, Co-, Ni-, Cu-, and Pd-doped carbon aerogels. The metal content of these samples was around 20 wt%, except in the case of the Pd-containing sample, where it was as high as 46 wt%. Mean crystallite size ranged from 12 to 40 nm and the surface areas from 370 to 450 m /g. The presence of some graphitic nanoribbons was detected in some of the prepared samples, as reported previously by other authors [42,51,55]. 

Erkey and co-workers [59-61] prepared Pt- and Ru-doped carbon aerogels using a supercritical deposition method. This involved dissolution of an organometallic precursor in a supercritical fluid and the exposure of a solid substrate to this solution. After impregnation of the support with the metal precursor, it was converted to the metal form by different methods. Dimethyl(l,5-cyclooctadiene) platinum(ll) was used as a precursor for Pt [59,60], and two different Ru complexes, trisacetylacetonate Ru(lll) and Ru(cod)(tmhd)2, were used for Ru [61], Monolithic organic and carbon aerogels... 

Nanocomposited carbon aerogels represent a different approach because of the organic nature of the precursory gel and the pyrolysis step [11]. In this case, high metal content can be achieved (up to 46% in the case of Pd-doped carbon aerogel)... 

Figure 21.9. Pt-doped carbon aerogel derived via copolymerization of a metal complex with the gel precursors image reprinted from [3], p. 2339, with permission from Elsevier.

Table 10.4 Surface Characteristics and Rate Constant (k) of NTS Photodegradation in the Presence of Metal-Doped Organic and Carbon Aerogels ...

Fig. 43. N2 adsorption-desoption isotherms at 77 K on three carbon aerogels, witliout (a) or with metal doping (b). Courtesy of Phof. K. Kaneko of Chiba Univ.

Studies on the behavior of chromium, molybdenum and tungsten oxide-doped monolithic carbon aerogels in the isomerization of 1-butene have been carried out by the group of Moreno-Castilla [38]. Samples were prepared by polymerization of a resorcinol-formaldehyde mixture which contained metallic salts of the elements and then the polymer was carbonized at both 500 and 1000 °C. The catalyhc performance of the samples was studied at temperatures ranging from 50 to 425 °C. 

Fig. 5.8 Synthesis of metal-doped organic and carbon aerogels (post-synthesis, impregnation).

Yoshizawa N, Hatori H, Soneda Y, Hanzawa Y, Kaneko K, Dresselhaus M S (2003) Structure and electrochemical properties of carbon aerogels polymerized in the presence of Cu. J Non-Cryst Solids 330 99-105 Maldonado-Hodar F J, Moreno-Castilla C, Perez-Cadenas A F (2004) Surface morphology, metal dispersion, and pore texture of transition metal-doped monolithic carbon aerogels and steam-activated derivatives. 

The physicochemical surface properties of Cr-, Fe-, Co-, Ni-, and Cu-doped monolithic organic aerogels and their carbonized and steam-activated derivatives were also studied [42-44]. These samples were prepared by adding chromium nitrate or metal acetates to an initial mixture with an R/F molar ratio of 0.5 and an R/W molar ratio of 0.13. The amount of metal added was that required to yield 1 wt% of the metal in the initial solution. 

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