Surface total acidity

Hydroxyl-Zr bentonite catalyst for esterification was prepared. Effects of the preparation conditions (calcination temperature, calcination time and ageing time) on interlayer distance, specific surface area and surface total acidity of catalyst have been studied. XRD, BET method and potentiometric titration were respectively used to detennine interlayer distance, specific surface area and surface total acidity of catalyst. Scanning Electron Microscopy was performed to observe the images of samples. 

Bentonite, whose main ingredient is montmorillonite, is one kind of layer structure clay mineral. It is an ideal material for preparation of pillared clays. If metal cations with high catalytic activity were intercalated in the interlayers of montmorillonite, a new type of solid acid catalyst can be obtained. The catalytic activity of the catalyst is closely associated with its porosity, specific surface area and surface total acidity. One of the effective ways to enhance catalytic activity is to prepare catalyst with appropriate metal cations and structure. 

The effects of preparation conditions on the surface total acidity... 

From Table 5 and Table 6 it can be seen that all the samples of different calcination time and aging time possess nearly the same acidity at a particular calcination temperature, revealing the negligible effect of the calcination time and aging time on the surface total acidity. However, Table 7 shows that the total number of acid sites and the number of the BrOnsted acid sites on the catalysts decrease with an increase in calcination temperature. It is known that the surface acid sites of hydroxyl-Zr bentonite mainly stem from surface hydroxyl and exposed metal cation [6], and the Bronsted acid sites result from protons on the surface of the octahedral layers. When the calcination temperature increases, the migration of protons to the octahedral layers of montmorillonite will become easier, leading to the decrease of the number of BrGnsted acid sites. 

Hydroxyl-Zr bentonite catalyst was prepared and characterized in our laboratory. The results show that the hydroxyl-Zr bentonite possesses good thermal stability. The interlayer distance of the modified bentonite deceased with the increase of aging time and its the specific surface area varies inversely with the calcination temperature but increases with the increase of aging time. The surface total acidity and the number of BrQnsted acid sites of hydroxyl-Zr bentonite are reduced with the increase of calcination temperature. 

Chemical composition was determined by elemental analysis, by means of a Varian Liberty 200 ICP spectrometer. X-ray powder diffraction (XRD) patterns were collected on a Philips PW 1820 powder diffractometer, using the Ni-filtered C Ka radiation (A, = 1.5406 A). BET surface area and pore size distribution were determined from N2 adsorption isotherms at 77 K (Thermofinnigan Sorptomatic 1990 apparatus, sample out gassing at 573 K for 24 h). Surface acidity was analysed by microcalorimetry at 353 K, using NH3 as probe molecule. Calorimetric runs were performed in a Tian-Calvet heat flow calorimeter (Setaram). Main physico-chemical properties and the total acidity of the catalysts are reported in Table 1. 

The alkylation of phenol investigated over H-MCM-22, H-ITQ-2 and H-MCM-36 showed that the delamelation and pillaring did not improve the catalytic activity and this was explained on the secondary processes taking place during the preparation of the corresponding materials, and which strongly affect the total acidity and the acidity on the external surface. Also, the composition of the reaction products is not influenced to a considerable extent by product shape selectivity effects. This seems to show that the tert-butylation reaction preferentially proceed at (or close to) the external surface of the zeolite layers. 

The effect of the Si/Al ratio of H-ZSM5 zeolite-based catalysts on surface acidity and on selectivity in the transformation of methanol into hydrocarbons has been studied using adsorption microcalorimetry of ammonia and tert-butylamine. The observed increase in light olefins selectivity and decrease in methanol conversion with increasing Si/Al ratio was explained by a decrease in total acidity [237]. 

The total acidity of the EIII-02 and EIII-03 samples is reduced as compared with the pure Zr-montmorillonite. However, the acid strength is enhanced. The lowest charge on the surface layer could explain this behaviour. 

Figure 17.14 Relationship between surface acidities ( Total acidity, O Lewis acidity) of 12.5% Mo03/A1203 catalyst nitrided at 773, 973, and 1173 K and the rate of carbazole HDN...

Figure 5.3. A humic acid macromolecule interacting with a surface of a clay mineral. The proposed macromolecular structure of the soil humic acid (HA) is based on the following common average characteristics of humic acids MW 6386 Da elemental analysis (%) C, 53.9 N, 5.0 H, 5.8 0,35.1 S, 0.5 C/N, 10.7 NMR information (%) aliphatic C, 18.1 aromatic C, 20.9 carbohydrate C, 23.7 metoxy C, 4.9 carboxylic C, 8.4 ketone C, 4.5 phenolic C, 4.2 functional groups (cmol/g) carboxyl, 376 phenol, 188 total acidity, 564. The structure was created using the ACD/ChemSketch program. [HA-clay complex Chen s group, unpublished (2008). Individual HA molecule Grinhut et al., 2007.]...

In order to compare the PMMA results with those obtained with the carboxylic acrylic latex, the concentration of surface carboxyls must be determined. Acid location analysis (5 was carried out for this purpose. Briefly, the latexes were titrated conductometrically with 0.1N NaOH followed by a titration of the aqueous phase from which the particles had been removed by centrifugation. The difference in the two titrations provided the distribution between surface and soluble acid. The deficit between the total acid thus determined and the concentration of acrylic acid used in the polymerization was termed "buried". Although some drift occurred in the conductance with time, an equilibration time of approximately 10 minutes per addition of sodium hydroxide was generally sufficient to yield stable readings. 

Figure 5. Fluorescence emission intensity of Py-Cl6/C monolayers on aluminum from solutions of 0.005M total acid concentration. Surface molar percentage of Py-C14 is also shown.

The distribution of surface acidity strength has been studied by measuring the differential adsorption heat of ammonia. The differential scanning calorimetry (Setaram DSC 111) and the FTIR spectrophotometry (Nicolet 740) have been simultaneously used in order to measure the heat associated with the neutralization of the acidic sites and the amount of chemisorbed base, respectively. Once the sample is saturated at 250 °C and the total acidity measurement is obtained as the amount of base used in the titration, the measurement of the total acidity has been verified by desorption of the base at programmed temperature (TPD). A ramp of 5 °C/min between 250 °C and 500 °C has been followed, with a He flow of 20 cm3/min and using the FTIR spectrophotometry for the measurement of the desorption products. 

Let the current pH be pH r and the pH to which it is to be adjusted (the destination pH) be pH. If pH, is greater than pH an acid is needed. No matter how insignificant, a natural water will always have an alkalinity in it. Alkalinities of surface water can vary from 10 to 800 mg/L (Sincere, 1968). Until it is all consumed, this alkalinity will resist the change in pH. Let the current total alkalinity l>e [A lgeq in gram equivalents per liter. Let the total acidity to be added be [A aM eti in gram equivalents per liter. 

The total surface concentration and intensity distribution of acidic and basic active sites are presented in Fig. 7.10. The total height of the stacked bars represents the total surface concentration of the acidic and basic active sites in millimoles per gram. The individual parts of the stacked bar correspond to the intensity distribution. As shown in Fig. 7.10, these data indicate that magnesium silicate has a total acidic and basic site concentration of 1.8 and 2.3 mM/g, respectively [17]. In comparison with other types of adsorbents used in frying oil (activated carbon, alumna [basic], alumina [neutral], alumina [acidic], bleaching earth, dia-tomaceous earth, and silica), magnesium silicate shows the highest values of total acidic and basic sites. 

They could remove the coat of waxes on the leaf surface, and so then the sea salt could penetrate into the cells and could kill the cells. I just wanted to know if this has been cleared in your country, or is it still in discussion The other point you mentioned quite rightly that NH 4 is no really neutralizing agent. In the soil it will be transformed into NO i, and nitric acid will contribute to acidity. The measurement of total acidity by just titrating the amount of acidity is a questionable thing. You have to determine the species of N0 3 and NH" 4 in the precipitation and add it to the acidity, so you have to do more than titrating... Well, I have a question what happens on the surface of leaves or other material in dry deposition of acids Maybe if you have a coat of SO2 which is then transformed into sulphuric acid, will this sulphuric acid be a permanent coat on the leaves and can nitric acid then be added to this ... 

In this work, the efTect of anodic oxidation treatments on activated carbon fibets (ACFs) was studied in the context of Cr(Vl), Cu( II), and Ni( II) ion adsorption behaviors. Ten wt% phosphoric acid and sodium hydroxide were used for acidic and basic electrolytes, respectively. Surf properties of the ACFs were determined by XPS. The specific surface area and the pore stnicture were evaluated from nitrogen adsorption data at 77 K. The heavy metal adsorption rates of ACFs were measured by using a UV spectrometer and 1C P. As a result, the anodic treatments led to an increase in the amount of total acidity by an increase of acidic functional groups such as carboxyl, lactone, and phenol, in spite of a decrease in specific surface area, due to the pore blocking by increased acidic functional groups. 

Walendziewski (75) observed that the total acidity per unit surface area of CoMoP/Al catalysts measured by NH3 TPD increases with increasing phosphorus loading (Fig. 25). Chadwick et al. (60) reported that the surface acidity of NiMoP/Al catalysts measured by pyridine adsorption increased slightly as a result of phosphorus addition. 

The combination of synthesis and modification techniques gives us a chance to rationally design or tailor zeolite structures. For example, we can increase shape selectivity by modifying or eliminating active sites on the external surface of zeolite crystals. Although this outside surface may represent only 2-5 % ot the total surface area, acid sites located there are more accessible to reacting molecules than acid sites in the pores. As these catalytic sites are not shape selective, they catalyze a disproportionate amount of non-shape selective reactions. 

Moffat and his co-workers have carried out several studies with phosphate catalysts and Moffat and Riggs prepared BPO4 catalysts for which H3PO4/H3BO3 varied from 1.0 to 1.5 and used them for propan-l-ol dehydration. Surface acidity was determined by n-butylamine titration and the rate constant was observed to increase as surface acidity increased this could have been an effect of either total acid strength or of a narrower range of strengths. It was also concluded that, as acid site concentration decreased with pre-treatment temperature, the main active sites must be Bronsted acid sites. 

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