Oxidation on Pt/alumina

Such a behaviour seems to be a characteristic of the CO-O2 reaction, since it was observed in our study with different active metals (Rh, Pt, Pd), different loadings, various catalyst shapes and with different superficial velocities and flow directions (upward and downward). Similar dynamics has been reported for the CO oxidation on Pt/alumina in a larger tubular reactor [7]. 

A possible mechanism for the effect of vanadia is suggested by the observation that vanadium oxide severely reduces the propensity of a Pt/alumina catalyst to store sulfate. It seems reasonable to speculate that SO2 oxidation on Pt/alumina involves adsorption of SO2 onto the alumina surface, with migration ( spillover ) of a sulfite species onto neighboring Pt crystallites and/or of oxygen atoms from the Pt onto the support. Coverage of alumina with high-valent vanadia can, because of its acidic nature, reduce affinity for SO2 and thereby disrupt the mechanism. 

Figure 3. Influence of promotion on Figure 4. Reaction rate and catalyst the conversion of l-methoxy-2 propa- potential during the oxidation of L-nol (Bi/Ptsurf = 0.2, Pb/Ptsurf = 0.3, sorbose on Pt/alumina and Bi/Pt/alu-Sn/Ptgurf = 0.13, Ag/PtSurf = 0.3) mina (Bi/Ptsurf= 0.5).

CO oxidation experiments were performed on Pt/alumina and Pt/ceria model catalysts, prepared by colloidal lithography. The samples were prepared without any of the additional plasma or UV-ozone pretreatments steps described in Preparation Procedures. Figure 4.38 shows T50 (the temperature at which 50% of reactant conversion is reached) and E (the apparent activation energy) as a function of CO oxidation cycle (ramping up and down in temperature). It is seen that both T50 and E initially shifts up during... 

CO oxidation in O2 excess on the fresh model catalyst. XPS analysis indicates stabilization of Pt oxide in the case of Pt/ceria [98]. In contrast, similar measurements on Pt/alumina show that these Pt particles are metallic and the chemical state does not change significantly after several CO oxidation cycles in O2 excess [98]. The long-term lean CO oxidation experiments on Pt/ceria indicate that the catalyst activity gradually changes as a function of CO oxidation experiment time. Extensive CO reduction causes an up-shift of both T50 and E a, which is attributed to C deposition on the catalyst [9], probably via CO disproportionation at CO excess. A lower value of T50 and E can, however, be restored by running a H2 oxidation over the catalyst (cycles 5-7) around stoichiometric conditions a = 0.67). The influ-... 

Figure 3. Conversion, selectivity, and yield of ethylene formation by ethane oxidation on Pt coated alumina ceramic foam monoliths. Up to 70% C2H4 selectivity is obtained at -70% C2H6 conversion for a single pass yield of -55%. Addition of Sn to Pt increases the selectivity and alkane conversion significantly.

The emission of nitrogen oxides (NOx) from automotive and stationary sources causes serious environmental concern. Automotive exhaust gas aftertreatment systems are commonly based on precious metal catalysts (three way or diesel oxidation catalysts). One undesired effect during NOx reduction with these catalysts is the formation of N2O, which is now considered to be an environmental pollutant also [1,2], In this report the generation of N2 and N2O during NOx decomposition or reduction on Pt/alumina is investigated. 

The time dependencies of the rates of three oxidation reactions at 873 K in the presence of HMDS vapor on Pt/alumina catalyst bead are illustrated in Figure 2. It can be seen that the rates of methane and propene oxidation are rapidly reduced in the presence of HMDS, but that there is negligible effect on hydrogen oxidation. 

FIGURE 17.3 Oxidation reactions on Pt/alumina catalysts with and without Cl. Left panel conversion versus temperature right panel Arrhenius plots. (A) CO oxidation. Data in broken line correspond to TOF recalculated using IR corrections. (B) CH4 oxidation. (C) CjHg oxidation. Feed composition 0.3% CO, CH4, or CjHg 16% O2, balance He. Total flow rate 130 cc/min. Recycle reactor. 

D. H. Kim, M. S. Lim, Kinetics of selective CO oxidation in hydrogen-rich mixtures on Pt/alumina catalysts. Appl. Catal. A... 

Figure 10.5. Comparisons of the conversion obtained on Ag/alumina in combination with Pt oxidation catalyst in the presence of hydrogen. 500 ppm NO, 375 ppm C8H18, 1 vol.% H2, 6 vol.% 02, 10vol.% C02, 350ppm CO, 12vol.% H20 in He. GHSV = 60000h 1 (reproduced with permission from Ref. [72]).

Platinum supported on carbon (Pt/C) was tested as solid catalysts in the oxidation of sucrose using molecular oxygen as oxidant (Scheme 10). The reaction was carried out in water and under atmospheric pressure. The support strongly influences the reaction and Pt/C was found more efficient than Pt/Alumina at 353 K. Over Pt/C, at a pH of 9, mono-, di-, and tricarboxylate derivatives were mainly obtained with a tricarboxylate yield of 35% [103]. 

Promotion and deactivation of unsupported and alumina-supported platinum catalysts were studied in the selective oxidation of 1-phenyl-ethanol to acetophenone, as a model reaction. The oxidation was performed with atmospheric air in an aqueous alkaline solution. The oxidation state of the catalyst was followed by measuring the open circuit potential of the slurry during reaction. It is proposed that the primary reason for deactivation is the destructive adsorption of alcohol substrate on the platinum surface at the very beginning of the reaction, leading to irreversibly adsorbed species. Over-oxidation of Pt active sites occurs after a substantial reduction in the number of free sites. Deactivation could be efficiently suppressed by partial blocking of surface platinum atoms with a submonolayer of bismuth promoter. At optimum Bi/Ptj ratio the yield increased from 18 to 99 %. 

Catalysts. - Group VIII metals, conventional base metal catalysts (Ni, Co, and Fe) as well as noble metal catalysts (Pt, Ru, Rh, Pd) are active for the SR reaction. These are usually dispersed on various oxide supports. y-Alumina is widely used but a-alumina, magnesium aluminate, calcium aluminate, ceria, magnesia, pervoskites, and zirconia are also used as support materials. The following sections discuss the base metal and noble metal catalysts in detail, focusing on liquid hydrocarbon SR for fuel cell applications. 

Weiland et al observed that a small amount of Pt metal present in the Rh-based catalyst could significantly improve the catalyst activity for ATR of gasoline range fuels. They claimed that the role of Pt is to enhance oxidation activity, whereas Rh provides high SR activity. The Rh-Pt/alumina catalyst used in the study was supported on monolithic honeycombs and had a Rh to Pt ratio of 3-10 by weight. The geometry (metal monolith, ceramic monolith, or ceramic foam) of the support did not affect the product composition. ... 

A. L. Boehm an, S. Niksa, and R. J. Moffatt, A Comparison of Rate Earnfor CO Oxidation Over Pt on Alumina, SAE 930252, Society of Automotive Engineers, Warrendale, Pa., 1993. 

Oxidation of hydrogen on a Pt/alumina particle in a batch recycle-flow reactor liraCek et al. (23) X... 

Pt/Al203 catalyst Oxidation of ethane on Pd/alumina catalyst Oxidation of CO on Wicke et al. (52) X ... 

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