Monometallic Ni Catalysts Research Articles

Catalytic performance and characterization of Pt–Ni bimetallic catalysts for oxidative steam reforming of methane

Effects of methane oxygen mixture addition to steam reforming of methane and subsequent removal of the methane oxygen mixture from the oxidative steam reforming of methane on catalytic performance were investigated using monometallic Ni and Pt catalysts and two Pt–Ni bimetallic catalysts. Hysteresis with respect to the addition and removal of the methane oxygen mixture was observed clearly on a Pt–Ni bimetallic catalyst prepared by co-impregnation method and the Ni catalyst. In contrast, no hysteresis was observed for a Pt–Ni catalyst that was prepared by sequential impregnation method. Combined with characterization results obtained using EXAFS analysis and FTIR of CO adsorption, Pt–Ni catalyst was prepared by sequential impregnation is formed Pt–Ni alloy particles, where Pt atoms are segregated on the surface, enhances the reducibility of Ni drastically and this is related to the behavior without hysteresis.

CO methanation over supported bimetallic Ni–Fe catalysts: From computational studies towards catalyst optimization

Abstract DFT calculations combined with a computational screening method have previously shown that bimetallic Ni–Fe alloys should be more active than the traditional Ni-based catalyst for CO methanation. That was confirmed experimentally for a number of bimetallic Ni–Fe catalysts supported on MgAl 2 O 4 . Here, we report a more detailed catalytic study aimed at optimizing the catalyst performance. For this purpose, two series of mono and bimetallic Ni–Fe catalysts supported on MgAl 2 O 4 and Al 2 O 3 , respectively, were prepared. All catalysts were tested in the CO methanation reaction in the temperature interval 200–300 °C, and characterized using elemental analysis, N 2 physisorption measurements, XRD and TEM. Optimization of the catalyst performance was made by varying the Ni:Fe ratio, the total metal loading and the support material. For both support materials, the bimetallic catalysts with compositions 25Fe75Ni and 50Fe50Ni showed significantly better activity and in some cases also a higher selectivity to methane compared with the traditional monometallic Ni and Fe catalysts. A catalyst with composition 25Fe75Ni was found to be the most active in CO hydrogenation for the MgAl 2 O 4 support at low metal loadings. At high metal concentrations, the maximum for the methanation activity was found for catalysts with composition 50Ni50Fe both on the MgAl 2 O 4 and Al 2 O 3 supports. This difference can be attributed to a higher reducibility of the constituting metals with increasing metal concentration. The maximum of the catalytic activity and the highest selectivity to methane were observed for the sample with 20 wt% total metal loading. It appears that it is possible to increase substantially the efficiency of Ni-based methanation catalyst by alloying with Fe.

Surface modification of Ni catalysts with trace Pt for oxidative steam reforming of methane

Hysteresis of catalytic performance with respect to temperature increasing and decreasing in oxidative steam reforming of methane (CH 4/H 2O/O 2/Ar = 40/30/20/10) over the monometallic Ni catalysts disappeared by the modification with Pt, and the additive effect of Pt by the sequential impregnation method (Pt/Ni) was much more significant than that by the co-impregnation method (Pt + Ni) in terms of catalytic performance and catalyst bed temperature profile. Characterization results by means of TEM, TPR, EXAFS, and FTIR suggest that the Pt atoms on the Pt/Ni catalysts were located more preferably on the surface to form a Pt Ni alloy than those on the Pt + Ni catalysts. The modification of Ni with Pt suppressed the oxidation of Ni species near the bed inlet in the oxidative steam reforming of methane at 1123 K, although the species on the monometallic Ni catalysts were oxidized under similar conditions. This can be due to the decreased oxidation rate of the species and the increased reduction rate caused by the surface modification of Ni with Pt. Consequently, the Pt Ni species can be maintained in the metallic state near the bed inlet, and the species can be the active site for the reforming reaction as well as the combustion reaction, which this leads to a lower bed temperature and smaller temperature gradient than those seen for the monometallic Ni catalysts.

06/00734 Addition effect of ruthenium on nickel steam reforming catalysts: Ishihara, A. et al. Fuel, 2005, 84, (12–13), 1464–1468.

Cu/ZrO2, Ni/ZrO2 and bimetallic Cu–Ni/ZrO2 catalysts were prepared by deposition–precipitation method to produce hydrogen by oxidative steam reforming of methanol (OSRM) reaction in the range of 250–360 °C. TPR analysis of the Cu–Ni/ZrO2 catalyst showed that the presence of Cu facilitates the reduction of the Ni at lower temperatures. In addition, this sample showed two reduction peaks, the former peak was attributed to the reduction of the adjacent Cu and Ni atoms which could be forming a bimetallic Cu-rich phase, and the second was assigned to the remaining Ni atoms forming bimetallic Ni-rich nanoparticles. Transmission Electron Microscopy revealed Cu or Ni nanoparticles on the monometallic samples, while bimetallic nanoparticles were identified on the Cu–Ni/ZrO2 catalyst. On the other hand, Cu–Ni/ZrO2 catalyst exhibited better catalytic activity than the monometallic samples. The difference between them was related to the Cu–Ni nanoparticles present on the former catalyst, as well as the bifunctional role of the bimetallic phase and the support that improve the catalytic activity. All the catalysts showed the same selectivity toward H2 at the maximum reaction temperature and it was ∼60%. The high selectivity toward CO is associated to the presence of the bimetallic Ni-rich nanoparticles, as evidenced by TEM–EDX analysis, since this behavior is similar to the one showed by the monometallic Ni-catalyst.

N-Hexane isomerization on Ni-Pt catalysts/supported on HUSY zeolite: The influence from a metal content

Bi-functional catalysts were prepared to contain Ni, Pt or both, supported on a HUSY zeolite, with the following metal contents: catalysts 30, 130 and 180 × 10 −6 atg metal/g catalyst. These catalysts resulted from a competitive ion exchange with the use of aqueous solutions from [Ni(NH 3) 6]Cl 2 and [Pt(NH 3) 4]Cl 2 complexes. The catalysts were provided with a scheduled temperature reduction (TPR) and subjected to a catalytic assessment on the n-hexane isomerization at 250 °C and 1 atm. TPR results showed larger reducibility of Ni +2 cations in the presence of Pt. Bi-metallic Ni-Pt catalysts showed to have smaller deactivation and much higher activity compared to monometallic Ni catalysts. The selectivity for the production of di-ramified alkanes increases as the Ni content increases.

Addition effect of ruthenium on nickel steam reforming catalysts

Several Ni-based catalysts supported on a mixture of MgO, La 2O 3, and Al 2O 3 were prepared. The catalytic performance in the steam reforming of m-cresol was evaluated. In the investigation of the effect of Ru loading added to the Ni-catalyst, it was found that the presence of Ru strongly enhances the catalytic performance of the Ni-based catalyst when increasing Ru loading up to 2 wt%. Effect of Ni loading to the Ru-based catalyst system was also investigated. It was found that the addition of nickel to the Ru-based catalyst up to 15 wt% enhanced significantly the catalytic activity of the catalyst. The lifetime of the Ru–Ni catalysts in the reforming of m-cresol was further tested at 750 °C. In agreement with general observations of the use of Ni monometallic catalyst, deactivation of the catalyst due to the carbon deposition reaction already occurred in the reforming of the oxygenated compound. On the other hand, a reasonable high resistant on the carbon deposition in the reforming of m-cresol was given by the 2 wt% Ru–15 wt% Ni catalyst system. An effort in improving the strength of the catalyst support with this catalyst system was also conducted, and the catalyst showed significant increase in the stability of the reforming of oxygenated aromatic compound.

Study of CO chemisorption on graphite-supported Ru–Cu and Ni–Cu bimetallic catalysts

The adsorption of CO on graphite-supported monometallic catalysts (Ni and Ru) and bimetallic catalysts (Ru–Cu and Ni–Cu) reduced at different temperatures was studied by microcalorimetry. The calorimetric profiles obtained over these two bimetallic systems provides information about the different types of interaction (bridged, linear or subcarbonyl species) that could exist in the bimetallic system when Cu was introduced in the Ru and Ni monometallic catalysts.

Thiophene hydrodesulfurization on sulfided Ni, W and NiW/USY zeolite catalysts: effect of the preparation method

The effect of the preparation method and metal loading on the hydrodesulfurization ⊙HDS) of thiophene, and on the dispersion and location of Ni and/or W species in Ni, W and NiW sulfides supported on USY zeolite, was investigated by temperature-programmed reduction ⊙TPR), X-ray photoelectron spectroscopy, N 2adsorption and acidity determination. The monometallic Ni catalyst prepared by ion exchange [Ni ⊙int)] exhibited higher initial HDS activity than those prepared by impregnation [Ni ⊙imp)] and by ion exchange and subsequent formation of small NiO clusters by NaOH treatment [Ni ⊙clus)]. For the binary NiW catalyst series with different metal contents, the catalysts prepared by impregnating W onto the Ni ⊙int) one showed activities comparable to those of the catalysts prepared by impregnating Ni onto the W/USY sample. These catalyst series showed much higher activities than those prepared by impregnating W onto the Ni ⊙clus). The characterization results revealed that catalysts displayed significant differences in dispersion, location and sulfidation of the Ni and W phases dependent on the preparation method. However, none of these factors alone accounted for the activity trend. In general, it was found that a combination of high acidity and metal dispersion led to catalysts with high initial HDS activity.

99/00207 Catalytic hydrogenation of aromatic hydrocarbons in a trickle bed reactor

The work presented in this paper is a continuation of our earlier work aimed at acquiring a fundamental understanding of sulfided Ni-Mo/γ-Al2O3catalysts in HDN catalysis. A series of temperature-programmed desorption and reduction experiments were performed overin-situsulfided bare γ-alumina support, alumina-supported monometallic Ni, Mo, and bimetallic NiMo catalysts. The TPD and TPR results were linked to the active site assignment of Ni- and Mo-associated centers in HDN reactions. Postreaction XPS and SEM characterizations were performed for catalysts used in HDN for up to 1000 h. One of the major changes during the aging of the Ni-Mo/γ-Al2O3catalysts was the loss of some active sites associated with the Ni promoters. The decreased Ni content over the catalyst surface was consistent with the observed decrease in the hydrogenation function of the catalyst. Two possible mechanisms are suggested for the loss of Ni active sites. One is coking that spreads from the alumina support to the nickel sites. Another is segregation of some Ni atoms from the Ni-Mo-S structure due to loss of structural sulfur.

NiMoS/γ-Al2O3Catalysts: The Nature and the Aging Behavior of Active Sites in HDN Reactions

The work presented in this paper is a continuation of our earlier work aimed at acquiring a fundamental understanding of sulfided Ni-Mo/γ-Al2O3catalysts in HDN catalysis. A series of temperature-programmed desorption and reduction experiments were performed overin-situsulfided bare γ-alumina support, alumina-supported monometallic Ni, Mo, and bimetallic NiMo catalysts. The TPD and TPR results were linked to the active site assignment of Ni- and Mo-associated centers in HDN reactions. Postreaction XPS and SEM characterizations were performed for catalysts used in HDN for up to 1000 h. One of the major changes during the aging of the Ni-Mo/γ-Al2O3catalysts was the loss of some active sites associated with the Ni promoters. The decreased Ni content over the catalyst surface was consistent with the observed decrease in the hydrogenation function of the catalyst. Two possible mechanisms are suggested for the loss of Ni active sites. One is coking that spreads from the alumina support to the nickel sites. Another is segregation of some Ni atoms from the Ni-Mo-S structure due to loss of structural sulfur.