abstracts - Институт катализа им. Г.К. Борескова

OP-III-30with an Anton Paar XRK900 reactor chamber. The samples were heated at a nominal rate of1°C/min, starting from 25°C and ending at 880°C in hydroden mixture: 5% H 2 -95% Ar andreactant mixture 1,67% O 2 - 3, 33% CH 4 - 95% Ar. The activity tests were carried out in thesame reactants stream (CH 4 /O 2 = 2/1) in temperature range 25 - 900°C with chromatographicanalysis. The XPS were recorded using a ES-300 Kratos Analitical electron spectrometer. XPspectra were taken with MgK α radiation (hν = 1253,6 eV), with analyzer pass energy 25eV.Specta were calibrated against E b (Au4f 7/2 )= 84,0 eV.Result and discussionResults of surface area measurements for Al 2 O 3 support and Ni-Au/Al 2 O 3 catalysts aftertheir calcination (4 h in air at 400 and 900°C) are presented in Table 1. Depending ontreatment temperature the specific surface area of Al 2 O 3 decreases from 130 to 80 m2/g andfor supported catalysts from 120 to 60 m2/g.Table 1 Influence of calcination temperature (4h in air) on specific surface area of Al 2 O 3support and 8%Ni-2%Au/ Al 2 O 3 catalysts.Calcination temperature [C°] Al 2 O 3 10%Ni/Al 2 O 3 8%Ni-2%Au/ Al 2 O 3400 130 110 112900 80 70 68TPRH2 profiles for 10%Ni/Al O and 8%Ni-2%Au/Al O catalysts after their2 3 2 3calcination 4h in air at 400°C and reoxidation at 600°C (after TPR run up to 900°C) arepresented as in Figure 1, respectively. TPR profiles differ considerably. Reduction of monometallicnickel oxide phase supported on Al O surface occur in temperature range 200 -2 3600°C whereas after catalyst reoxidation reduction effects are observed only above 800°C.Gold addition does not change considerably TPR profile for bimetallic Ni-Au catalyst thus,preventing nickel aluminate formation. Results of “in situ” XRD measurements representingtemperature programmed reduction behavior of NiO-Au mixture is illustrated in Figure 2 A.One can see that reduction of NiO starts at about 200°C and is accomplished bellow 300°C.Above 500°C, the characteristic gradual shift of XRD lines is observed. Above 850°C onlyXRD lines assigned to alloy of Ni-Au phase are visible. In Figure 2 B there are shown theXRD patterns after: reduction of NiO-Au mixture in the conditions of POM reaction and itsreduction in 5% H 2 – 95% Ar atmosphere, and finally, for working 8% Ni-2% Au/Al2O3catalyst in the conditions of POM reaction. One can conclude that bimetallic Ni - Au alloyformation takes place in the conditions of both, POM reaction and hydrogen reduction at880°C. XPS spectra for 8% Ni-2% Au/Al2O 3 catalyst are presented in Figure 3 and they weretaken after: reduction at 500°C, calcination at 400°C and finally, after POM reaction at 850°C.One can see that for all samples metallic nickel, metallic gold and nickel oxides are present on catalystsurface. Complex structure of XPS patterns seems to indicate that nickel as well as gold can appear indifferent forms. On the other hand the existence of Ni-Au alloy can be inferred. Catalyst activity testsindicate that gold addition considerably lowers the ignition temperature of POM reaction from 850 to750°C. In the temperature range 400 - 700°C the total oxidation of methane dominates whereas for Ni387