Hydrogenation gas-phase

The thermal conductivity of gas-phase deuterium is about 0.73 times that of gas-phase hydrogen. This thermal conductivity difference offers a convenient method for analysis of H2—D2 mixtures. Other physical properties of D2, T2, HD, DT, and HT are Hsted in the Hterature (60). 

The removal of C4-acetylenes may be effected by catalytic gas-phase hydrogenation in a gas-particle operation by a process similar to that widely used for removing acetylene from ethylene streams. However, in view of the strong polymerization tendency of the C4-fractions, it is desirable in this case to work at the lowest possible temperature. 

The degree of dissociation is very small but the diphenylcyanomethyl radical is sufficiently reactive to induce polymerization in styrene. Methyl radicals or hydrogen atoms bring about polymerization of vinyl monomers in the gas phase.Hydrogen peroxide in the presence of ferrous ions initiates polymerization in the aqueous phase or in aqueous emulsions through generation of hydroxyl radicals according to the Haber-Weiss mechanism... 

The WGS reaction is a reversible reaction, that is, it attains equilibrium with reverse WGS reaction. Thus the fact that the WGS reaction is promoted by H20(a reactant), in turn, implies that the reverse WGS reaction may also be promoted by a reactant, H2 or CO2. In fact the decomposition of the surface formates produced from H2+CO2 is promoted 8-10 times by gas-phase hydrogen. The WGS and reverse WGS reactions can conceivably proceed on different formate sites of the ZnO surface unlike usual catalytic reaction kinetics, while the occurrence of the reactant-promoted reactions does not violate the principle of microscopic reversibility[63]. 

For presulfided Co.Mo/Si02-Al203, the formation and elimination of the add sites were almost the same as those observed for non-sulfided Ck>.Mo/Si02-Al203. Presufidation with hydrogen sulfide did not affect much the conversion of the acid sites caused by gas phase hydrogen. 

The recovery of the Lewis add sites and the decrease in the protonic acid sites to the original values by outgassing gas phase hydrogen are rather slow and require a high temperature. The addition of Pt/Si02 did not affect much the restoration of Ae Lewis add sites of H-ZSM-5 by outgassing gas phase hydrogen. 

WiESSMEiER, G., Honigke, D., Heterogeneously catalyzed gas-phase hydrogenation of cis,trans,trans-1,5,9-cyclododecatriene on palladium catalysts having regular pore systems,... 

Figure3.58 Experimental results for partial gas-phase hydrogenation of, 5,9-cyclododecatrienein a Ptmicro-channel reactor[l 30],...

Figure3.60 Gas-phase hydrogenation ofl, 5-cyclooctadiene. Conversion and selectivitydependingon hydrogen partial pressure[l 30],...

Expressions for 9 SM and H2 can be derived and related to rate (k) and equilibrium constants (K). The SI and S2 site balances are 9SM +9a + S, = 1 and //2 + S2 = 1 respectively 9sx, S2 are empty sites). Based on Henry s law, the gas-phase hydrogen pressure and the liquid-phase hydrogen concentration may be used interchangeably. The rate expression can be written as follows ... 

The amounts of exchange and addition were calculated from a hydrogen isotope mass balance of the coal products, donor solvent and gas phase hydrogen. The starting and product weights of the coal and hydrogen compositions of the coal and coal products are shown in Table IV. From the values in Table IV, the net amount of hydrogen added to the coal, H, is... 

This parameter takes into account the presence of inerts, the use of nonstoichiometric quantities of reactants, and the presence of one or more of the reaction products in the original system. To illustrate this point, let us consider as an example the isothermal gas phase hydrogenation of ethylene (C2H4 + H2 - C2H6) taking... 

A gas-phase hydrogenation reactioa C2H (A) + H2 - C2H6, is conducted under isothermal and isobaric conditions in a CSTR The feed, consisting of equimolar amounts of each reac-... 

As a final example of catalytic hydrogenation activity with polymer-stabilized colloids, the studies of Cohen et al. should be mentioned [53]. Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films. The organometallic repeat-units contained in the polymer were reduced by exposing the films to hydrogen at 100 °C, leading to the formation of nearly monodisperse Pd nanoclusters that were active in the gas phase hydrogenation of butadiene. 

The WGS reaction is a reversible reaction that is, the WGS reaction attains equilibrium with the reverse WGS reaction. Thus, the fact that the WGS reaction is promoted by H20 (a reactant), in turn implies that the reverse WGS reaction may also be promoted by a reactant, H2 or C02. In fact, the decomposition of the surface formates produced from H2+C02 was promoted 8-10 times by gas-phase hydrogen. The WGS and reverse WGS reactions conceivably proceed on different formate sites of the ZnO surface unlike usual catalytic reaction kinetics, while the occurrence of the reactant-promoted reactions does not violate the principle of microscopic reversibility. The activation energy for the decomposition of the formates (produced from H20+CO) in vacuum is 155 kJ/mol, and the activation energy for the decomposition of the formates (produced from H2+C02) in vacuum is 171 kJ/mol. The selectivity for the decomposition of the formates produced from H20+ CO at 533 K is 74% for H20 + CO and 26% for H2+C02, while the selectivity for the decomposition of the formates produced from H2+C02 at 533 K is 71% for H2+C02 and 29% for H20+C0 as shown in Scheme 8.3. The drastic difference in selectivity is not presently understood. It is clear, however, that this should not be ascribed to the difference of the bonding feature in the zinc formate species because v(CH), vav(OCO), and v/OCO) for both bidentate formates produced from H20+C0 and H2+C02 show nearly the same frequencies. Note that the origin (HzO+CO or H2+C02) from which the formate is produced is remembered as a main decomposition path under vacuum, while the origin is forgotten by coadsorbed H20. 

M. Mons, I. Dimicoli, and F. Piuzzi, Gas phase hydrogen bonded complexes of aromatic molecules Photoionization and energetics. Int. Rev. Phys. Chem. 21, 101 135 (2002). 

Hofstadler, S.A. Sannes-Lowery, K.A. Griffey, R.H. Enhanced Gas-Phase Hydrogen-Deuterium Exchange of Oligonucleotide and Protein Ions Stored in an External Multipole Ion Reservoir. J. Mass Spectrom. 2000, 55, 62-70. 

Detailed microwave spectroscopic analysis of gas-phase hydrogen-bonded adducts can yield the hydrogen-bond energy with precision, e.g. for HCN HF, (NHF) = 26.1 1.6kJmol-i (Legon et al 1980). Sadly, few systems are susceptible to this approach. 

Although the gas-phase hydrogen-bonded dimer (MeF)2H" is held by a strong hydrogen bond (McMahon and Kebarle, 1986) this is a rare exception to the previous statement regarding covalently bonded fluoride. More typical are the perfluorocarbons, which are among the weakest hydrogenbonding substances known, as their physical properties and uses clearly demonstrate. 

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