Solid acids acid strength

In the present article, the discussion concentrates on the catalytic activity and selectivity of solid metal sulfates in terms of the acidic property (acidity, acid strength, and Bronsted and Lewis acids) by integrating the kinetic and structural studies. 

Absorption In chemistry, the process by which one substance, such as a solid or liquid, takes up another substance, such as a liquid or gas, through minute pores or spaces between its molecules. In physics, the process in which the incident radiated energy is retained without reflection or transmission on passing through a medium ACC Aerogel Cherenkov Counter Acidity Acid strength... 

Oleum is marketed in all strengths up to ca. 70 per cent. SO3. From 0 to 40 per cent, free SO3, it is a liquid from 40 to 60 per cent, free SO3, it is a solid from 60 to 70 per cent, free SO3, it is liquid above 70 per cent, free SO3, it is a solid. The acid must be kept in ground glass stoppered, thick-walled bottles. If it is required to melt the acid, the stopper is removed, a watch glass placed on the mouth of the bottle, and the bottle placed in a layer of sand in an air bath which is warmed with a small flame. The bottle is fitted with a wash bottle attachment, and any desired quantity of acid is forced out by gentle air pressure from a hand or foot bellows (the mouth must not be used) this procedure is far more satisfactory than that of pouring the liquid acid from the bottle. 

Perfluorinated carboxylic acids are corrosive liquids or solids. The acids are completely ionized in water. The acids are of commercial significance because of their unusual acid strength, chemical stabiUty, high surface activity, and salt solubiUty characteristics. The perfluoroaLkyl acids with six carbons or less are hquids the higher analogues are soHds (Table 1). 

Shape selective catalysis as typically demonstrated by zeolites is of great interest from scientific as well as industrial viewpoint [17], However, the application of zeolites to organic reactions in a liquid-solid system is very limited, because of insufficient acid strength and slow diffusion of reactant molecules in small pores. We reported preliminarily that the microporous Cs salts of H3PW12O40 exhibit shape selectivity in a liquid-solid system [18]. Here we studied in more detail the acidity, micropore structure and catal3rtic activity of the Cs salts and wish to report that the acidic Cs salts exhibit efficient shape selective catalysis toward decomposition of esters, dehydration of alcohol, and alkylation of aromatic compound in liquid-solid system. The results were discussed in relation to the shape selective adsorption and the acidic properties. 

When the temperature is increased at 550 °C, the water removed from the solid reduces Ni2+ to Ni+. The formation of the monovalent nickel cations by thermal reduction of Ni2+-exchanged Y zeolite has been detected using the IR spectroscopy of CO adsorption [9]. The NH3-TPD measurements have evidenced that the acid sites strength strongly... 

Other information is provided in Tables 3-8. This includes values of log Ch -for use with equation 17 for HCIO4 and HC1 these are simply the log acid molarity, assuming the acid to be fully dissociated. The maximum acid strength is 80 wt% for HCIO4, at which point the acid mixtures become solid at 25°C, and 40% for HC1, at which point the aqueous solution is saturated with the... 

Another thermal analysis method available for catalyst characterization is microcalorimetiy, which is based on the measurement of the heat generated or consumed when a gas adsorbs and reacts on the surface of a solid [66-68], This information can be used, for instance, to determine the relative stability among different phases of a solid [69], Microcalorimetiy is also applicable in the measurement of the strengths and distribution of acidic or basic sites as well as for the characterization of metal-based catalysts [66-68], For instance, Figure 1.10 presents microcalorimetry data for ammonia adsorption on H-ZSM-5 and H-mordenite zeolites [70], clearly illustrating the differences in both acid strength (indicated by the different initial adsorption heats) and total number of acidic sites (measured by the total ammonia uptake) between the two catalysts. 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

Figure 13.2 Acid strength of acid and superacid solids determined by Hammet method. For a comparable purpose, the acid strengths of some liquid acids are also included. (After Ref. 12.)...

In the case of C4-hydrocarbons, the use of acid or superacid solids will depend on both the acid strength required in each reaction and the reaction conditions required to optimize the thermodynamic equilibrium (Figure 13.3). For example, catalysts with very high acid strength could be substituted for a solid with a lower acidity by increasing reaction temperature. This has been proposed in both the isomerization of lineal alkanes and in the alkylation of isobutene with olefins, although the thermodynamic equilibrium should also be considered. 

In conclusion, more efficient and clean solid (acid and superacid) catalysts will be used in the coming years to reduce not only the emission of environmentally harmful products but also the use of noxious catalysts. The optimal catalytic systems will be determined from the nature of acid strength of its active sites, the nature of the reaction, and the reaction conditions. 

In addition, a new physicochemical method to characterize the acid strength of acid and superacid solids also will be required in order to evaluate and compare acid strengths with those obtained with liquid acids. 

As a result, the acid strength of the proton is approximately equivalent to that of sulfuric acid in nonaqueous media. In view of the excellent miscibility of this anion with organic nonpolar materials, Armand et al. proposed using its lithium salt (later nicknamed lithium imide , or Lilm) in solid polymer electrolytes, based mainly on oligomeric or macro-molecular ethers. In no time, researchers adopted its use in liquid electrolytes as well, and initial results with the carbonaceous anode materials seemed promising. The commercialization of this new salt by 3M Corporation in the early 1990s sparked considerable hope that it might replace the poorly... 

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