(617hg) Kinetics and Spectroscopic Studies of Methane Partial Oxidation on Ni and Rh Catalysts

Kinetics and Spectroscopic studies of
Methane Partial Oxidation on Ni and Rh Catalysts

Cun Wen, Jason Hattrick-Simpers, Jochen Lauterbach_,*

University of South
Carolina, Columbia, SC, 29208, USA

*Corresponding author: lauteraj@cec.sc.edu

Recent exploration of shale gas has led to shockwaves in
both energy markets and academic research fields. On the basis of same amount
of energy content, shale gas has a much lower price (about 70% lower) compared
with that of crude oil, even with todayfs low crude-oil price at $40 per barrel.
The price difference between shale gas and crude oil has revived interests to
convert methane, as the major component in shale gas, to gasoline and diesel.
Methane partial oxidation (POM), in particular, is an preferred processed due
to its optimum H₂ to CO ratio of 2 for downstream Fischer-Tropsch
synthesis and mild heat release. However, the most active catalyst for POM is Rh,
which is a nobel metal catalyst with a much higher price tag compared with the
next best candidate in-line, Nickle. Here, fundamental studies that compares
the reaction kinetics and reaction mechanism between Ni and Rh will be
presented, and the possibility of design an Ni catalyst possessing comparable
activity of Rh will be discussed.

Series of Rh and Ni catalysts using ƒÁ-Al₂O₃
as supports were synthesized by following literature.[1,
2] The structures of two catalyst were characterized with ICP, XRD, BET, TEM,
to make sure they have comparable metal loadings, particle size, surface area.
Their catalytic activity for POM were compared under the same reaction
conditions. Consistently with literature,[1,
3] the Rh catalysts showed activity toward POM (T₅₀= 502 ‹C) at a
temperature about 100 ‹C lower than that on Ni catalysts (T₅₀= 605
‹C). The catalytic activity of Rh and Ni catalysts were widely reported to be
limited by methane dissociation as the rate-determining step.[4,
5] Therefore, methane-temeprature programmed reduction experiments were design
to compare how easily methane can be activated and dissociated by Rh and Ni
catalysts. In contrary to the catalytic activity tests, the Rh and Ni catalysts
possessed comparable starting temperature for CH₄ dissociation at
around 200‹C, as shown in Figure 1. Furthremore, Ni catalysts had no activity
toward POM until 450 ‹C, at which temperature CH₄ could readily
dissociate on the Ni catalysts accroding to CH₄-TPR. More detailed
kinetics and spectroscopic results indicate that Ni catalysts can be partially
oxided under the POM condition with CH₄ to O₂ ratio of
0.5, and loss the activity toward POM. More importantly, methodologies to
increase the resistence of Ni to oxidation will be discussed in this
presentation.

Figure 1. Methane-temperature programmed reduction
on a) Rh/Al₂O₃ and b) Ni/Al₂O₃
catalysts.

References:

1.         Li, J.-M., et al., Effect of Rh
loading on the performance of Rh/Al2O3 for methane partial oxidation to
synthesis gas. Catalysis Today, 2008. 131(1–4): p. 179-187.

2.         Jin,
R., et al., Mechanism for catalytic partial oxidation of methane to syngas
over a Ni/Al2O3 catalyst. Applied Catalysis A: General, 2000. 201(1):
p. 71-80.

3.         Dissanayake,
D., et al., Partial oxidation of methane to carbon monoxide and hydrogen
over a Ni/Al2O3 catalyst. Journal of Catalysis, 1991. 132(1): p.
117-127.

4.         Wei,
J. and E. Iglesia, Isotopic and kinetic assessment of the mechanism of
reactions of CH4 with CO2 or H2O to form synthesis gas and carbon on nickel
catalysts. Journal of Catalysis, 2004. 224(2): p. 370-383.

5.         Wei,
J. and E. Iglesia, Structural requirements and reaction pathways in methane
activation and chemical conversion catalyzed by rhodium. Journal of
Catalysis, 2004. 225(1): p. 116-127.