Basicity Carbonate, oxide group

A part of the oxygen not accounted for is bound in basic surface oxides which are present on any carbon. The structure of these groups has not been satisfactorily explained so far. Their chemistry seems important in oxygen transfer reactions. 

Oxidation and incorporation of nitrogen usually affect the surface chemistry of carbons [12, 20, 24]. The types and numbers of basic and acidic groups evaluated using Boehm titration [3, 4]. are collected in Table 2. The data reported indicate that the initial carbons differ in their acidity as a result of the activation method and the type of an organic precursor [1]. BAX is more acidic than BPL. This is expected for a phosphoric acid activated carbon [25]. After modification with urea and heat treatment at 723 and 1223 K, the overall surface chemistry... 

The various groups differ in their acidity and basicity, and the carbon surface acquires acidic and/or basic properties, depending on the nature of the sur ce functionahty. It is known for a long time that a given carbon can have either acidic or basic surface character, depending on its pretreatment [39, 40], In the following, the acidic and basic surface oxides will be discussed in detail. 

Voll, M. and Boehm, H.-P. (1971). Basic surface oxides on carbon — IV. Chemical reactions for the identification of surface groups (in German). Carbon, 9, 481-8. Garten, V.A. and Weiss, D.E. (1957). Ion and electron exchange properties of activated carbon in relation to its behaviour as a catalyst and adsorbent. Ren. Pure Appl. Chem., 1, 69-122. 

Copper can also be used as a catalyst, like nickel, alone, on carriers, or as a mixed catalyst with metals of the first to the eighth Group of the Periodic Table. The temperature needed for reduction of the catalyst, usually containing the copper as oxide, hydroxide, or basic carbonate, is 150-300°. Preparation of a copper-kieselguhr catalyst is similar to that of a nickel-kieselguhr catalyst.175... 

Successive experimental mns carried ont with the same AC sample in the ozone decomposition showed that the smface chemistry is important only in the first cycles of reaction, dne to a slightly progressive oxidation of the smface, which provokes the loss of basic smface gronps and an increase of acidic groups, mainly carboxylic acids [166-168]. This led Sanchez-Polo et al. [167] and Alvarez et al. [168] to propose that AC conld not be a catalyst for ozone decomposition, bnt rather, an initiator of the O3/H2O2 system. Faria et al. [166] concluded that basic carbons tended to behave as acid ACs upon losing activity, which were shown still to be active catalysts. Nevertheless, Gniza et al. 

Carbon materials have also been used in environmental catalysis for the removal of SO, NO c, and H2S from gaseous streams. Basic carbons were the most active in these processes, particularly N-doped carbons. Linear correlations between the catalytic activity and the concentration of pyridinic groups were reported in the oxidation of SO2 and in the selective catalytic reduction of NO with ammonia. 

---