Passivity nickel

Antimony-based passivation was introduced by Phillips Petroleum in 1976 to passivate nickel compounds in the FCC feed. Antimony is injected into the fresh feed, usually with the help of a carrier such as light cycle oil. If there are feed preheaters in the unit, antimony should be injected downstream of the preheater to avoid thermal decomposition of the antimony solution in the heater tubes. 

Antimony is a metal, in either hydrocarbon or aqueous solution, commonly injected into the fresh feed to passivate nickel. 

In many aqueous solutions nickel has the ability to become passive over a wide range of pH values. The mechanism of passivation of nickel and the properties of passive nickel have been studied extensively—perhaps more widely than for any other element, except possibly iron. In recent years the use of optical and surface analytical techniques has done much to clarify the situation . Early studies on the passivation of nickel were stimulated by the use of nickel anodes in alkaline batteries and in consequence were conducted in the main in alkaline media. More recently, however, attention has been directed to the passivation of nickel in acidic and neutral as well as alkaline solutions. 

SURECAT A method for prereducing and passivating nickel catalysts. Developed in 1990 by Eurocat for ATOCHEM. 

Using the unique four-electrode STM described above, Bard and coworkers (Lev, 0. Fan, F-R.F. Bard, A.J. J. Electroanal. Chem.. submitted) have obtained the first images of electrode surfaces under potentiostatic control. The current-bias relationships obtained for reduced and anodically passivated nickel surfaces revealed that the exponential current-distance relationship expected for a tunneling-dominated current was not observed at the oxide-covered surfaces. On this basis, the authors concluded that the nickel oxide layer was electrically insulating, and was greater than ca. 10 A in thickness. Because accurate potential control of the substrate surface is difficult in a conventional, two-electrode STM configuration, the ability to decouple the tip-substrate bias from... 

J.R. Rostrup-Nielsen, Sulphur-Passivated Nickel Catalysts for Carbon-Free Steam Reforming of Methane , J. Catal., 85 31-43 (1984). 

Poisoning of metal catalysts may provide a tool for improving selec> tivity by affecting the concentrations of ensembles required by different reaction paths. This is illustrated by steam reforming on sulfur passivated nickel catalysts and the results are compared with observations for sulfided platinum-rhenium catalysts for catalytic reforming and for a chlorine poisoned palladium catalyst for partial oxidation of methane. 

STEAM REFORMING ON SULFUR PASSIVATED NICKEL CATALYSTS... 

Rostrup-Nielsen JR (1984) Sulfur-passivated nickel-catalysts for carbon-free steam reforming of methane. J Catal 85 31... 

As an example, the experimental results for the anodic dissolution of alloys of the nickel-chromium system are presented in Figs 5 and 6. This composition is the basis of several superalloys, which are machined using the ECM. Alloy components - chromium and nickel - exhibit different tendencies to passivate. Nickel is weakly passivated in the NaCl solution its tendency to passivate is much stronger... 

In the following, examples of the ensemble control by means of adsorbed poisons are discussed with the the emphasis on steam reforming of methane on sulfur passivated nickel catalysts. The conclusions for ensemble control will be compared with data for catalytic reforming on PtRe(S) catalysts and for the impact of chlorine on partial oxidation of methane on Pd-catalysts. 

Several experimental results support the adsorption mechanism for stationary conditions of the passive layer. Even the stationary passive current density depends on the composition of the electrolyte. For iron in 0.5 M H2SO4, the passive current density is 7 pA cm , whereas less than lpAcm is detected in 1 M HCIO4. From these observations, a catalysis for the transfer of Fe + from the passive layer to the electrolyte by S04 ions was concluded [55, 56]. Similarly, the dissolution Ni + from passive nickel and nickel base alloys is accelerated by organic acids hke formic acid and leads to a removal of NiO from the passive layer [57]. Additions of citrate to the electrolyte cause the thinning of passive layers on stainless steel and increase its Cr content [58]. Apparently Fe and Ni ions are complexed at the surface of the passive film, which causes an enhancement of their dissolution into the electrolyte. It should be mentioned that the dissolution of Cr " " apparently is not catalyzed by these anions and remains... 

Gu, L., Y. W. Wang, R. Lu, L. Guan, X. S. Peng, and J. Sha. 2014. Anodic electrodeposition of a porous nickel oxide-hydroxide film on passivated nickel foam for supercapacitors. Journal of Materials Chemistry A 2 7161-7164. 

In this section, we discuss atomistic modeling studies of the interaction of model passivated surfaces with halide ions. First, the study using conventional DFT of chloride adsorption and subsurface penetration on defect-free hydroxylated nickel oxide surfaces characteristic of passivated nickel surfaces is presented. Then the implications of using DFT-l-U are discussed as well as the interaction with other halides. This is followed hy one example on the effect of implementing surface defects characteristic of those observed experimentally on a passivated nickel surface. Finally, the application of reactive MD modeling to more complex systems including a substrate metal (copper) covered by a passive film (copper oxide) in interaction with a chloride-containing aqueous solution is presented. 

Morris, P. E. and Scarberry, R. C., Anodic Polarization Measurements of Active-Passive Nickel Alloys by Rapid-Scan Poten-tiostatic Techniques, Corrosion, Vol. 26, No. 7, July 1970, pp. 169-179. 

Nickel, copper, and silver as powdered samples rapidly heated in NF3 (20°C per minute in a differential scanning calorimeter) appear to become passivated nickel at about 330°C, copper at 270 to 340°C, and silver at 350°C [17]. 

An example of reaction steps for a passive film formation is given below. According to Burstein [13], a passive nickel (Ni) oxide film may form through... 

Type 316,317 stainless steel (passive) Type 304 stainless steel (passive) Type 410 stain less steel (passive) Nickel (passive)... 

Passive Nickel and the Point Defect Model The passive state of nickel shows much more complicated behavior than for iron in the same solutions. A minimum of... 

M. Keddam, H. Takenouti, and N. Yu, New data on the kinetics of passive nickel from very low frequency impedance measurements, Corros. Sci. 27 107 (1987). 

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