Nickel steam reforming catalyst

This is not exactly what the speaker had in mind In 2007, we are faced with the potential severity of the problem encapsulated by the cartoon what is as yet not clear is whether STM might provide the necessary molecular insight to designing an appropriate catalyst just as the Aarhus Topsoe group achieved in their development of the nickel gold steam-reforming catalyst. 

Diffraction patterns from a nickel-alumina steam reforming—methanation catalyst and a sample of sintered nickel recorded on a LIN AC source... 

Nickel-based steam reforming catalysts are very efficient for the decomposition of tars and ammonia in biomass gasification gas. Ceramic candle filters can be applied to remove particles at high temperature. It is proposed to use nickel-activated alumina candle filters for the simultaneous removal of tar, ammonia and particles from biomass gasification gas [12]. 

The feed is desulfurized and mixed with process steam before entering the steam reformer. This steam reformer is a top-fired box type furnace with a cold outlet header system developed by Krupp Uhde. The reforming reaction occurs over a nickel catalyst. Outlet reformed gas is a mixture of H2, CO, C02 and residual methane. It... 

Steam reforming was the primary reaction over these nickel catalysts. The presence of hydrocarbons (G2 to G5) which would indicate cracking reactions occurred to the extent of less than 10% in the reaction products. The presence of methane, which would indicate partial reforming, did not exceed 5% in the reaction products. There does not appear to be any significant difference in product selectivity for the n-hexane steam reforming reaction over nickel on the 2 quite different supports—zeolite vs. alumina. Carbonaceous residues accumulated in the case of all the nickel catalysts where reforming activity was sustained and the carbon deposition on the zeolite catalysts compared favorably with G56. 

The addition of potassium to a nickel/ -alumina steam reforming catalyst provides resistance to the accumulation of carbonaceous deposits in two ways. First, the alkali reduces the rate of hydrocarbon cracking on the nickel component of the catalyst. Second, the promoter enhances the rate of the steam gasification of carbon on the catalyst. This is accomplished by increasing the surface coverage of water on the catalyst and hence supplementing the pre-exponential component of the gasification rate equation. 

Aptly named, this process treats a mixture of hydrocarbons (propane, CjHg, is shoAvn as a representative example) from natural gas or crude oil with steam (700°C- 1000°C) over a nickel catalyst and reforms it into a mixture of CO and H2 gases, which is called synthesis gas, or just syngas. The second reaction is knovra as the water-gas shift reaction, perhaps because it shifts oxygen from one reactant to another and thereby adjusts the composition of the syngas. It is carried out at elevated temperatures (325-350°C) over an iron(III) oxide catalyst. 

Steam Reforming. When relatively light feedstocks, eg, naphthas having ca 180°C end boiling point and limited aromatic content, are available, high nickel content catalysts can be used to simultaneously conduct a variety of near-autothermic reactions. This results in the essentiaHy complete conversions of the feedstocks to methane ... 

Methane. The largest use of methane is for synthesis gas, a mixture of hydrogen and carbon monoxide. Synthesis gas, in turn, is the primary feed for the production of ammonia (qv) and methanol (qv). Synthesis gas is produced by steam reforming of methane over a nickel catalyst. 

Nickel catalysts are also used for steam methane reforming. Moreover, nickel catalysts containing potassium to inhibit coke formation from feedstocks such as LPG and naphtha have received wide appHcation. 

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

Na.tura.1 Ga.s Reforma.tion. In the United States, most hydrogen is presently produced by natural gas reformation or methane—steam reforming. In this process, methane mixed with steam is typically passed over a nickel oxide catalyst at an elevated temperature. The reforming reaction is... 

Steam Reformings of Natural Gas. This route accounts for at least 80% of the world s methanol capacity. A steam reformer is essentially a process furnace in which the endothermic heat of reaction is provided by firing across tubes filled with a nickel-based catalyst through which the reactants flow. Several mechanical variants are available (see Ammonia). 

In the catalytic steam reforming of natural gas (see Fig. 2), the hydrocarbon stream, principally methane, is desulfurized and, through the use of superheated steam (qv), contacts a nickel catalyst in the primary reformer at ca 3.04 MPa (30 atm) pressure and 800°C to convert methane to H2. 

Tubular Fixed-Bed Reactors. Bundles of downflow reactor tubes filled with catalyst and surrounded by heat-transfer media are tubular fixed-bed reactors. Such reactors are used most notably in steam reforming and phthaUc anhydride manufacture. Steam reforming is the reaction of light hydrocarbons, preferably natural gas or naphthas, with steam over a nickel-supported catalyst to form synthesis gas, which is primarily and CO with some CO2 and CH. Additional conversion to the primary products can be obtained by iron oxide-catalyzed water gas shift reactions, but these are carried out ia large-diameter, fixed-bed reactors rather than ia small-diameter tubes (65). The physical arrangement of a multitubular steam reformer ia a box-shaped furnace has been described (1). 

Steam Reforming Processes. In the steam reforming process, light hydrocarbon feedstocks (qv), such as natural gas, Hquefied petroleum gas, and naphtha, or in some cases heavier distillate oils are purified of sulfur compounds (see Sulfurremoval and recovery). These then react with steam in the presence of a nickel-containing catalyst to produce a mixture of hydrogen, methane, and carbon oxides. Essentially total decomposition of compounds containing more than one carbon atom per molecule is obtained (see Ammonia Hydrogen Petroleum). 

Figure 8.3.1 is a typical process diagram for tlie production of ammonia by steam reforming. Tlie first step in tlie preparation of tlie synthesis gas is desulfurization of the hydrocarbon feed. Tliis is necessary because sulfur poisons tlie nickel catalyst (albeit reversibly) in tlie reformers, even at very low concentrations. Steam reforming of hydrocarbon feedstock is carried out in tlie priiiiiiry and secondary reformers. 

The operation of a large synthetic ammonia plant based on natural gas involves a delicately balanced sequence of reactions. The gas is first desulfurized to remove compounds which will poison the metal catalysts, then compressed to 30 atm and reacted with steam over a nickel catalyst at 750°C in the primary steam reformer to produce H2 and oxides of carbon ... 

A major route for producing synthesis gas is the steam reforming of natural gas over a promoted nickel catalyst at about 800°C ... 

Many late transition metals such as Pd, Pt, Ru, Rh, and Ir can be used as catalysts for steam reforming, but nickel-based catalysts are, economically, the most feasible. More reactive metals such as iron and cobalt are in principle active but they oxidize easily under process conditions. Ruthenium, rhodium and other noble metals are more active than nickel, but are less attractive due to their costs. A typical catalyst consists of relatively large Ni particles dispersed on an AI2O3 or an AlMg04 spinel. The active metal area is relatively low, of the order of only a few m g . ... 

Cold-Nickel Alloy Catalysts for Steam Reforming... 

Figure 8.7 confirms that this is correct A single nickel catalyst used for steam reforming of n-butane deactivates steadily and gains weight due to the accumulation of carbon, but a Ni-Au catalyst maintains its reforming activity at a constant level [F. Besenbacher, I. ChorkendorfF, B.S. Clausen, B. Hammer, A.M. Molenbroek, J.K. Norskov and I. Stensgaard, Science 279 (1998) 1913]. 

Nickel catalysts used in steam reforming are more resistant to deactivation by carbon deposition if the surface contains sulfur, or gold. Explain why these elements act as promoters. Would you prefer sulfur or gold as a promoter Explain your answer. 

Several other important commercial processes need to be mentioned. They are (not necessarily in the order of importance) the low pressure methanol process, using a copper-containing catalyst which was introduced in 1972 the production of acetic add from methanol over RhI catalysts, which has cornered the market the methanol-to-gasoline processes (MTG) over ZSM-5 zeolite, which opened a new route to gasoline from syngas and ammoxidation of propene over mixed-oxide catalysts. In 1962, catalytic steam reforming for the production of synthesis gas and/or hydrogen over nickel potassium alumina catalysts was commercialized. 

Because of a great practical importance of SMR as a major industrial process for manufacturing H2, the development of efficient steam reforming catalysts is a very active area of research. Nickel and noble metals are known to be catalytically active metals in the SMR process. The relative catalytic activity of metals in the SMR reaction (at 550°C, 0.1 MPa and steam/carbon ratio of 4) is as follows [12] ... 

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