Methane zeolite catalysts

A zeolite catalyst operated at 1 atm and 325-500 K is so active that the reaction approaches equilibrium. Suppose that stack gas having the equilibrium composition calculated in Example 7.17 is cooled to 500 K. Ignore any reactions involving CO and CO2. Assume the power plant burns methane to produce electric power with an overall efficiency of 70%. How much ammonia is required per kilowatt-hour (kWh) in order to reduce NO , emissions by a factor of 10, and how much will the purchased ammonia add to the cost of electricity. Obtain the cost of tank car quantities of anhydrous ammonia from the Chemical Market Reporter or from the web. 

In the direct ammoxidation of propane over Fe-zeolite catalysts the product mixture consisted of propene, acrylonitrile (AN), acetonitrile (AcN), and carbon oxides. Traces of methane, ethane, ethene and HCN were also detected with selectivity not exceeding 3%. The catalytic performances of the investigated catalysts are summarized in the Table 1. It must be noted that catalytic activity of MTW and silicalite matrix without iron (Fe concentration is lower than 50 ppm) was negligible. The propane conversion was below 1.5 % and no nitriles were detected. It is clearly seen from the Table 1 that the activity and selectivity of catalysts are influenced not only by the content of iron, but also by the zeolite framework structure. Typically, the Fe-MTW zeolites exhibit higher selectivity to propene (even at higher propane conversion than in the case of Fe-silicalite) and substantially lower selectivity to nitriles (both acrylonitrile and acetonitrile). The Fe-silicalite catalyst exhibits acrylonitrile selectivity 31.5 %, whereas the Fe-MTW catalysts with Fe concentration 1400 and 18900 ppm exhibit, at similar propane conversion, the AN selectivity 19.2 and 15.2 %, respectively. On the other hand, Fe-MTW zeolites exhibit higher AN/AcN ratio in comparison with Fe-silicalite catalyst (see Table 1). Fe-MTW-11500 catalyst reveals rather rare behavior. The concentration of Fe ions in the sample is comparable to Fe-sil-12900 catalyst, as well as... 

Supported palladium oxide is the most effective catalyst used in total methane oxidation and in catalytic oxidation of VOCs [1-5]. However, the activity of the conventional catalysts is not sufficient [5-6]. Recently, the Pd-zeolite catalysts have attracted considerable attention due to their high and stable CH4 conversion efficiency [4-8]. In this work, the effect of the preparation method, the nature of the charge-balancing cations, the palladium loading and the pre-treatment gas nature on the texture, structure and catalytic activity of the Pd-ZSM-5 solids are investigated. 

G.V. Echevsky, E.G. Kodenev, O.V. Kikhtyanin, V.N. Parmon, Direct Insertion of Methane into C3-C4 Paraffins Over Zeolite Catalysts a Start to the Development of New One-Step Catalytic Processes for Gas to Liquid Transformation, 258, Applied Catalysis A General, 159-171, (2004). 

Methane dehydroaromatization on zeolites Mo/HZSM-5 was also investigated by solid-state MAS NMR spectroscopy 162. Both variation of the state of the transition metal component and products (such as ethane, benzene, and ethylene) adsorbed in zeolite were observed after reaction at high temperature (900-1000 K). Molybdenum carbide species, dispersed on the external surface or in the internal channels of the zeolite catalysts, had formed during the reaction 162. ... 

The chain length of n-alkanes has a marked influence on reactivities for hydroisomerization, and especially for hydrocracking. To a very small extent a methane and ethane abstracting mechanism, probably hydrogenolysis as predicted in a basic work on bifunctional catalysis (14), is found to be superimposed when lower carbon number feeds (C, Cg, Cg) are used. n-Hexane is excluded from ideal hydrocracking. On the Pt/Ca-Y-zeolite catalyst it is cracked via a mechanism that is mainly hydrogeno-lytic. 

The thermal and catalytic conversion of different hydrocarbon fractions, often with hydrotreating and other reaction steps, is characterized by a broad variety of feeds and products (Table 1, entry 4). New processes starting from natural gas are currently under development these are mainly based on the conversion of methane into synthesis gas, further into methanol, and finally into higher hydrocarbons. These processes are mainly employed in the petrochemical industry and will not be described in detail here. Several new processes are under development and the formation of BTX aromatics from C3/C4 hydrocarbons employing modified zeolite catalysts is a promising example [10],... 

Destruction of N20 can be carried out at lower temperatures by adding a reductant. In this case an iron-containing zeolite catalyst is used for the selective catalytic reduction of N20 using hydrocarbons as a reductant. The catalyst did not deactivate in a 2000-hour test under demanding conditions (450°C, 6% H20). Hydrocarbons such as propane (or LPG) and methane (widely available as natural gas) can be used as the reducing agent221. 

Heterogeneous catalysts activate C—H bonds at significantly higher temperatures. For example, a Fe/Co modified Mo-supported acidic ZSM-5 zeolite catalyst dehydrogenates methane under non-oxidizing conditions at 700°C to a mixture of Q-C4 alkanes/alkenes and Q-Q2 aromatics such as benzene and naphthalene.140... 

Metal oxides on zeolites have also found use as redox catalysts. High-temperature (700-750 °C) dehydroaromatization of methane under nonoxidizing conditions has been explored with a number of zeolitic catalysts modified with transition metal ions. Although coke formation at these high temperatures is a problem, calcined molybdate-impregnated ZSM-5 shows unparalleled activity of up to 8 % methane conversion with 100 % selectivity towards aromatics. Surface studies of these Mo HZSM-5 catalysts indicate that M0O3 crystals are on the external zeolite surface [123]. 

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. 

Activation and aromatization of methane and ethane over Mo(VI)/HZSM-5 and W(VI)/HZSM-5 zeolites catalysts... 

Detail studies were carried out on Fe-ZnO and Fe-ZnO/zeolite catalyst further more. Hydrocarbon synthesis from CO2 over various Fe-ZnO/zeolite catalyst is shown in Table 2. By the addition of HY zeolite, the formation of olefins and the selectivity of C2+ hydrocarbon increased and that of methane decreased. The hydrocarbon distribution of Fe-ZnO and Fe-ZnO/HY is shown in Figure 2. Hydrocarbon distribution followed Schulz-Rory rule over Fe-ZnO catalyst, indicating F-T reaction took place. However, it changed to the formation of higher hydrocarbons over Fe-ZnO/HY, indicating MTG reaction took place. 

Hydrogenation of C02 over Rh ion exchanged zeolite catalysts (RhY) was studied. The RhY catalyst showed high activity for hydrogenation of C02. The main product transformed from methane to CO and formation of ethanol was promoted in accordance with Li addition. Characterization of surface sites and adsorbed species was performed. 

Careful control of the precipitation allows the pore size distributions of amorphous materials to be controlled rather well, but the distributions are still much broader than those in the zeolite catalysts. This limits the activity and selectivity. One effect of the reduced activity has been that these materials have been applied only in making middle distillates diesel and turbine fuels. At higher process severities, the poor selectivity results in production of unacceptable amounts of methane (CH4) to butane (C4H10) hydrocarbons. 

Initial experiments performed at the INL compared different catalysts, fluids, and operating conditions to determine the effect of SCF on solid acid catalyst alkylation (5). Three sets of studies were performed a catalyst comparison using six different catalysts (i.e., two zeolites, two sulfated metal oxides, and two Nafion catalysts) with methane as a cosolvent an exploration of the effect of varying methane addition on alkylation using a USY zeolite catalyst and a study of the effect of seven cosolvents (i.e., three hydrocarbons, two fluorocarbons, carbon dioxide, and sulfur hexafluoride) at L, ML, NC-L, and SCF conditions on the USY catalyst performance. 

Direct Decomposition of Methane to Hydrogen on Metal-Loaded Zeolite Catalyst... 

The results obtained indicated that for Ni/Na-Y Zeolite catalyst (the most acidic support) for the range of variable studied, the effective order of the reaction 1s zero with respect to methane, positive with respect to steam and negative with respect to hydrogen. For Ni/Ni A120, the effective order is positive with respect to steam and methane and negative with respect to hydrogen. 

Not surprisingly, the zeolites which deactivate fastest appear to be the ones with a one dimensional, or quasi one dimensional, pore system. Furthermore it appears that there is a high correlation between fast deactivation and a mainly methane producing catalyst. 

---