Sulfuric acid adsorption

Catalytic gas-phase reactions play an important role in many bulk chemical processes, such as in the production of methanol, ammonia, sulfuric acid, and nitric acid. In most processes, the effective area of the catalyst is critically important. Since these reactions take place at surfaces through processes of adsorption and desorption, any alteration of surface area naturally causes a change in the rate of reaction. Industrial catalysts are usually supported on porous materials, since this results in a much larger active area per unit of reactor volume. 

Nishihara C and Nozoye H 1995 influence of underpotentiai deposition of copper with submonolayer coverage on hydrogen adsorption at the stepped surfaces Pt(955), Pt(322) and Pt(544) in sulfuric acid solution J. Electroanal. Chem. 396 139-42... 

As worldwide attention has been focused on the dangers of acid rain, the demand to reduce sulfur dioxide [7446-09-5] emissions has risen. Several processes have been developed to remove and recover sulfur dioxide. Sulfur can be recovered from sulfur dioxide as Hquid sulfur dioxide, sulfuric acid, or elemental sulfur. As for the case of hydrogen sulfide, sulfur dioxide removal processes are categorized as adsorption, absorption, or conversion processes. 

Isolation. Isolation procedures rely primarily on solubiHty, adsorption, and ionic characteristics of the P-lactam antibiotic to separate it from the large number of other components present in the fermentation mixture. The penicillins ate monobasic catboxyHc acids which lend themselves to solvent extraction techniques (154). Pencillin V, because of its improved acid stabiHty over other penicillins, can be precipitated dkecdy from broth filtrates by addition of dilute sulfuric acid (154,156). The separation process for cephalosporin C is more complex because the amphoteric nature of cephalosporin C precludes dkect extraction into organic solvents. This antibiotic is isolated through the use of a combination of ion-exchange and precipitation procedures (157). The use of neutral, macroporous resins such as XAD-2 or XAD-4, allows for a more rapid elimination of impurities in the initial steps of the isolation (158). The isolation procedure for cephamycin C also involves a series of ion exchange treatments (103). 

Herteto E, FeUu JM, Aldaz A. 1995a. CO adsorption and oxidation on Pt(l 11) electrodes modified by irreversibly adsorbed bismuth in sulfuric acid medium. J Catal 152 264-274. 

Figure 13.6 Potential-step electro-oxidation of formaldehyde on a Pt/Vulcan thin-film electrode (7 p,gpt cm, geometric area 0.28 cm ) in 0.5 M H2SO4 solution containing 0.1 M HCHO upon stepping the potential from 0.16 to 0.6 V (electrolyte flow rate 5 pL at room temperature). (a) Solid line, faradaic current transients dashed line, partial current for HCHO oxidation to CO2 dotted line, difference between the net faradaic current and that for CO2 formation, (b) Solid line, m/z = 44 ion current transients gray line potential-step oxidation of pre-adsorbed CO derived upon HCHO adsorption at 0.16 V, in HCHO-free sulfuric acid solution, (c) Current efficiency transients for CO2 formation (dashed line) and formic acid formation (dotted line).

Wolter O, Heitbaum J. 1984. The adsorption of CO on a porous Pt-electrode in sulfuric acid studied by DEMS. Ber Bunsenges Phys Chem 88 6-10. 

Another important catalytic technology for removal of NOx from lean-burn engine exhausts involves NOx storage reduction catalysis, or the lean-NOx trap . In the lean-NOx trap, the formation of N02 by NO oxidation is followed by the formation of a nitrate when the N02 is adsorbed onto the catalyst surface. Thus, the N02 is stored on the catalyst surface in the nitrate form and subsequently decomposed to N2. Lean NOx trap catalysts have shown serious deactivation in the presence of SOx because, under oxygen-rich conditions, SO, adsorbs more strongly on N02 adsorption sites than N02, and the adsorbed SOx does not desorb altogether even under fuel-rich conditions. The presence of S03 leads to the formation of sulfuric acid and sulfates that increase the particulates in the exhaust and poison the active sites on the catalyst. Furthermore, catalytic oxidation of NO to N02 can be operated in a limited temperature range. Oxidation of NO to N02 by a conventional Pt-based catalyst has a maximum at about 250°C and loses its efficiency below about 100°C and above about 400°C. 

The amounts oi adsorption of the polymer on latex and silica particles were measured as follows. Three milliliters of the polymer solution containing a known concentration was introduced into an adsorption tube(lO ml volume) which contained 2 ml of latex (C = l+.O wt %) and silica(C = 2.0 wt %) suspensions. After being rotated(l0 rpm) end-over-end for 1 hr in a water bath at a constant temperature, the colloid particles were separated from the solution by centrifugation(25000 G, 30 min.) under a controlled temperature. The polymer concentration that remained in the supernatant was measured colorimetrically, using sulfuric acid and phenol for the cellulose derivatives(12), and potassium iodide, iodine and boric acid for PVA(13). From these measurements, the number of milligrams of adsorbed polymer per square meter of the adsorbent surface was calculated using a calibration curve. 

Platinum was determined in seawater by adsorptive cathodic stripping voltammetry in a method described by Van den Berg and Jacinto [531]. The formazone complex is formed with formaldehyde, hydrazine, and sulfuric acid in the seawater sample. The complex is adsorbed for 20 minutes at -0.925 V on the hanging mercury drop electrode. The detection limit is 0.04 pM platinum. 

PuraSiv S A process for removing sulfur dioxide from the tail gases from sulfuric acid manufacture by adsorption on a special zeolite. Not to be confused with PuraSiv HR, Type S. 

The adsorption operation was conducted by feeding 1 mM phosphate solutions to the conditioned column at SV 10 or 20 h 1, and then 20 BV of water at SV 3 h 1. The elution operation consisted of feeding 0.1 M NaOH solution (80 BV) and then 20 BV of water at a flow rate of SV 3 h1. The regeneration of the column was conducted by feeding 0.5 M sulfuric acid (20 BV) and 20 BV of water at SV 10 h"1. All column effluents including washings in the adsorption and elution operations were collected on a fraction collector, and concentrations of phosphorus and zirconium in each fraction were determined by ICP-AES. Volume of each fraction was 5 BV for the adsorption operation and 4 BV for the elution operation. However, column effluents in regeneration operations were not analyzed. 

The only difference from the method (i) was in the regeneration operation. Here, the regeneration operation was conducted by supplying 0.5 M sulfuric acid (5 BV), 0.5 M sulfuric acid containing zirconium sulfate at 0.01 M (10 BV), 0.5 M sulfuric acid (15 BV) and water (20 BV) in successive at SV 10 h1. The adsorption and elution operations were almost the same as those in the method (i). 

The cyclic voitammogram for Pt (111) in 5 M sulfuric acid is shown in Fig. 2-21. Compared with that in 0.5 M sulfuric acid (Fig. 2-15), the anodic part of the two split hydrogen adsorption-desorption areas was compressed in the cathodic direction and became two sharp peaks while the cathodic part did not change its shape very much. The asymmetric peak at 700 mV shifted cathodicly and became more symmetric and sharp. The oxidation of platinum shifted about 100 mV in the anodic direction. All these changes could be attributed to the increase in specific adsorption of anions or the decrease of the activity of water as well as the pH change. 

Voltammograms of Ptdll) with and without COad adsorption in 0.5 M perchloric add are shown in Fig. 2-25. The voltammogram without CO was considerably different from those in sulfuric acid. The symmetric features in the range from 600 to 800 mV correspond to the anodic portion of the two split area of hydrogen adsorption-desorption in sulfuric add. Hydrogen adsorption-desorption features did not change after the oxidation peak at 1050 mV and its reduction while the further oxidation removes the feature irreversibly. Therefore the peak at 1050 mV is considered as a formation of a weak interaction with water. 

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