Partial oxidation of methanol

3 Partial oxidation of methanol Copper-zinc catalysts 

Copper-zinc catalysts have been found to be very active for the partial oxidation of methanol.142 

The onset of the partial oxidation reaction is 488 K and the rates of methanol and oxygen conversion increased strongly with temperature to 

Kinetic isotope effects using CH3OH and CH3OD show that the O-H bond is at least partially involved in the rate-limiting step. TPD experiments with pure Cu°, pure ZnO, and the catalyst Cu/ZnO showed that methanol can be activated by both ZnO and copper. On the ZnO surface, methanol can form intermediates, which in the presence of copper might react and desorb more easily probably via a reverse spillover process. The isotopic product distribution of H2, HD, D2,H20, HDO and D2O in the 

8 Temperature dependence of CH3OH conversion during temperature-programmed start-up over the Cu/ZnO/Al2C 3 catalyst in different initial states (o), oxidized ( ), reduced ( ), reduced + air exposed. Atmospheric pressure, feed ratio O2/CH3OH = 0.3, heating rate = O.lK/min (after Ref. 152). 

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A packed-bed nonpermselective membrane reactor (PBNMR) is presented by Diakov et al. [31], who increased the operational stability in the partial oxidation of methanol by feeding oxygen directly and methanol through a macroporous stainless steel membrane to the PB. Al-Juaied et al. [32] used an inert membrane to distribute either oxygen or ethylene in the selective ethylene oxidation. By accounting for the proper kinetics of the reaction, the selectivity and yield of ethylene oxide could be enhanced over the fixed-bed reactor operation. 

The present work demonstrates that the mixed oxide catalyst with inhomogeneous nanocrystalline MosOu-type oxide with minor amount of M0O3- and Mo02-type material. Thermal treatment of the catalyst shows a better performance in the formation of the crystals and the catalytic activity. The structural analysis suggests that the catalytic performance of the MoVW- mixed oxide catalyst in the partial oxidation of methanol is related to the formation of the M05O14 t3 e mixed oxide. 

Formaldehyde (F) is made by partial oxidation of methanol (M). A side reaction of formaldehyde to CO and H20 (W) also occurs. Approximate forms of the two rate equations are... 

Hydrogen adsorption is decreased because poisoning adsorbates stemming from partial oxidation of methanol blocks the hydrogen adsorption sites. 

This sui ests faster COad oxidation to CO2. As it was shown in Chapter 2 that high area platinum has sites for eoCOad (Easily Oxidized COad)> those sites may play a role in the oxidation of COad formed as the resTilt of partial oxidation of methanol. 

Catalytic partial oxidation of methanol can be expressed by the following equation ... 

Activity Measurements. To test catalytic properties of various samples partial oxidation of methanol to formaldehyde was studied in a flow micro-reactor operating under normal atmospheric pressure (10). For each run about 0.2 g of catalyst sample was used and the activities were measured at 173 C in the absence of any diffusional effects. The feed gas consisted of 72, 2 and by volume of nitrogen, oxygen and methanol vapor respectively. Reaction products were analysed with a 10% Carbowax 20 M column (2m long) maintained at 60 C oven temperature. 

Partial oxidation of methanol was used as a test reaction to study the oxidation activity of the catalysts in relation to vanadia loadings. These studies were carried out at a low temperature (173 C) in order... 

Monolayer coverage of vanadium oxide on tin oxide support was determined by a simple method of low temperature oxygen chemisorption and was supported by solid-state NMR and ESR techniques. These results clearly indicate the completion of a monolayer formation at about 3.2 wt.% V2O5 on tin oxide support (30 m g" surface area). The oxygen uptake capacity of the catalysts directly correlates with their catalytic activity for the partial oxidation of methanol confirming that the sites responsible for oxygen chemisorption and oxidation activity are one and the same. The monolayer catalysts are the best partial oxidation catalysts. 

In this communication, the results of a systematic study of ammonia chemisorption on V2O -Ti02 (anatase) catalysts of different vanadia loading is reported." Low temperature oxygen chemisorption is also utilized to determine the monolayer loading of 20 on Ti02 (anatase). Partial oxidation of methanol to formaldehyde is studied as a model reaction on these catalysts and the activities of the catalysts are correlated with NH and O2 uptakes. 

Although liquid hydrogen, LH2, can be used as a fuel source, much of the recent fuel cell research is focusing on the partial oxidation of methanol, natural gas, ethanol, or gasoline to produce the necessary hydrogen. Catalysts that aid in the partial oxidation of these fuels yields a readily available, rich source of hydrogen. Water is the primary exhaust emission produced by fuel cell powered vehicles. If a carbon-based fuel source is utilized, then a carbon-containing by-product will also be produced. 

These properties make CoTAA a good catalyst for the anodic oxidation of formic acid. Economic application of this catalyst is, however, not anticipated because formic acid is not economically attractive as a fuel. It is certainly possible to prepare electrodes containing a mixture of tungsten carbide and CoTAA as catalyst, with the tungsten carbide catalyzing the first stage of the oxidation of CH2O to HCOOH, and the CoTAA the further oxidation of HCOOH to CO 2, but this possibility does not offer any more favorable prospects. Economic application of CoTAA will only come into question when cheap catalysts are available for the partial oxidization of methanol to formaldehyde or formic acid. 

Synthesis and characterization of a new Sn-incorporated CoAl-layered double hydroxide (LDH) and catalytic performance of Co-spinel microcrystallites in the partial oxidation of methanol... 

M(lI)AlSn-LDHs with M(II) being Mg, Ni or Co were synthesized by a coprecipitation method. The influence of Sn on the thermal transformations and redox properties were investigated in detail using XRD, TG/DTA, SEM, TPR, 1 l9Sn-MAS NMR and UV-visible diffuse-reflectance (DR) spectroscopy methods. Some of these samples calcined at 450 °C were tested as catalysts in the partial oxidation of methanol (POM) reaction. In this paper we discuss briefly the effect of Sn-incorporation on the structural features and reducibility of CoAI-LDH. The catalytic performance of Co-spinel microcrystallites derived from CoAl-, and CoAlSn-LDHs was also evaluated. 

Sn-incorporation on the structural and redox properties of the CoAl-LDHs. The catalytic activity of spinel catalysts obtained from these LDH precursors has been tested in the partial oxidation of methanol (POM) to H2 fuel for fuel cells. 

The use of Cl sources in applied catalysis research has grown enormously in the past few years. The fact, that methanol can be conveniently synthesized from methane or coal, has promoted research into the reactions involving methanol. Partial oxidation of methanol to H2... 

Partial oxidation of methanol over CoAl-, and CoAISn-LDHs calcined at 450 °C/5h... 

The results of catalytic partial oxidation of methanol over the spinel catalysts derived from CoAl- and CoAISn-LDH are presented in Table 2. A methanol conversion of 30 to 50 mol % was obtained over catalyst derived from CoAI-LDH. The products obtained were H2, H20, CO and C02. Other products such as formaldehyde, methyl formate or dimethyl ether was not observed under the present experimental conditions. The selectivity of H20 was very high (= 40 to 60 %), probably because of the involvement of the complete oxidation of methanol over these catalysts. It is interesting to note from the Table that the methanol conversion rate and the selectivity of CO2 increased over the catalyst derived from the Sn-containing analogue. The observation that only traces of CO is produced in the Sn-containing catalyst, is attractive for the development of catalyst for POM reaction to produce H2 for fuel cell applications. The only inconvenience is the higher selectivity of H2O by complete oxidation, probably because of the higher Co content in the sample. 

In conclusion, a new Sn-incorporated CoAI-LDH has been synthesized. The effect of Sn-incorporation on the thermal transformation into spinels and their reducibility are investigated. Incorporation of Sn diminishes reducibility of Co species because of the enhanced polarization of Co-0 bonds. The Sn-containing spinel exhibits better catalytic performance in the partial oxidation of methanol to produce H2 and CO2 useful for fuel cells. 

Hydroxide (LDH) and Catalytic Performance of Co-spinel Microcrystallites in the Partial Oxidation of Methanol S. Velu and K. Suzuki... 

A disadvantage of the system is the considerable volumes of connecting tubing and the recycle pump. Large free volumes become unacceptable when homogeneous reaction or reactions on the tube walls occur. To use a ventilator that has the required capacity but can only work satisfactorily at relatively low temperatures, the gas from the reactor must be cooled and reheated before being returned to the catalyst bed. This procedure was a problem in a study of the partial oxidation of methanol to formaldehyde, where paraformaldehyde tended to be formed in the cooler parts of the recycle loop [43]. 

PF/PF Isothermal Shell side Partial oxidation of methanol Song Hwang, 1991... 

The process of catalytic partial oxidation of methanol with air in a fuel-rich mixture has been commercialized to produce formaldehyde since about 1890. Various catalysts have been used but silver catalyst is by far most widely used. Song and Hwang [1991] used a packed-bed porous membrane tubular reactor wi the catalyst packed on the shell side. They used a model consmicted essentially from Equations (10-36) and (10-44) with the permeation terms replaced by some terms similar to Equation (10-56) and k- =0. The partial oxidation of methanol can be conveniently described by... 

Figure 10.10 Effect of space time on conversion of partial oxidation of methanol in a porous Vycor glass membrane reactor (350 C, 60% air) [Song and Hwang, 1991]...

The partial oxidation of methanol to formaldehyde over metal oxides is important industrially, and the results of experiments done in the transient regime are summarized for M0O3 (249). The results in Fig. 41 show that the conversion of methanol and the selectivity toward formaldehyde in a Mars-van Krevelen process are both favored by a relatively oxidized surface. Weber (250) has shown by theoretical calculations that the surface methoxy intermediate should lose one of its hydrogens as a hydride ion attracted to Mo and not as a hydrogen atom or proton attracted to a doublely bonded or bridging oxygen. 

The advantage of the partial oxidation of methanol of supported metal oxides compared to neat oxides has been shown by transient and steady-state kinetic studies (251). Other recent progress in this field has been discussed (252). Another transient study involves various copper catalj sts (255), and particularly noteworthy in this study was the observation of responses to oscillation of the feed composition and the development of self-sustained oscillations. 

Schwedock, M. J., L. C. Windes, and W. H. Ray, Steady state and dynamic modelling of a packed bed reactor for the partial oxidation of methanol to formaldehyde-H. Experimental results compared with model predictions, Chem. Eng. Commun., 78, 45-71 (1989). 

Velu, S., Suzuki, K., and Osaki, T. Selective production of hydrogen by partial oxidation of methanol over catalysts derived from CuZnAl-layered double hydroxides. Catalysis Letters, 1999, 62 (2), 159. 

Agrell, J., Germani, G., Jaras, S.G., and Boutonnet, M. Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique. Applied Catalysis. A, General, 2003, 242 (2), 233. 

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