Investigation on Reverse Water-gas Shift over La2NiO4

Catalyst by cw-Cavity Enhanced Absorption Spectroscopy during CH4/CO2 Reforming

B.S. Liu, Ling Li, C.T. Au1, A.S.-C. Cheung Department of Chemistry, The University of Hong Kong, Pokfulam Road,

Hong Kong, China

1Department of Chemistry and Centre for Surface Analysis and Research, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China

Supported by the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 7101/02P).

Background

CO2 reforming : CH4 + CO2 → 2CO +2H2

catalyst

Methane is available in huge quantity, besides burning, there are many way to utilize it .

Coupling reaction: CH4 + CH4 C2H6 + etc…

Synthesis gas

Steam reforming: CH4 + H2O → CO + 3H2 Synthesis gas

Aromatization: nCH4 C6H6 , C10H8 + …

Background

CH4 + CO2 → 2CO +2H2 cat.

Numerous studies on CH4/CO2 reforming reaction using Ni-based catalysts.

CO2 + H2 CO + H2O

Synthesis gas

Problems: (i) Low yield ( ~55%)

(ii) Carbon deposit (~after 1 hour)

Our studies:

Reverse water-gas shift (RWGS) reaction over La2NiO4

catalyst during CH4/CO2 reforming by continuous wave

cavity enhanced absorption spectroscopy (CEAS).Associated reaction:

Experimental Setup for CEAS

Experimental Conditions:

Catalyst:

Ni(NO3)2· 6 H2O + HNO3 + La2O3 ’ La2NiO4 ’ + · · ·

50 mg ‘La2NiO4 ’sol-gel-generated catalyst at >500 oC

Laser system:

Tunable diode laser: 1279-1341 nm, 5 mWLinewidth: 5 MHz

High reflective mirror: R > 0.99995

Wavenumber (cm -1)

7510.5 7510.8 7511.1 7511.4

= H2O = CH4

2000 s

1500 s

1000 s

500 s

CEA spectra of CH4 and H2O obtained at different pulsing rate (of

CH4/CO2 reaction. (Temperature = 700 oC)

Results

HITRAN Data Base

CH4 7510.59 – 7511.20

H2O 7511.30

102 1

03

1031

01

Molecule Absorption (cm-1)Vibrationaltransition Rotational

J =0 (Q branch)

J = 5, Ka = 0, Kc= 5

J = 6, Ka = 2, Kc= 4

Wavenumber (cm -1)

7510.5 7510.8 7511.1 7511.4

= H2O = CH4

2000 s

1500 s

1000 s

500 s

CEA spectra of CH4 and H2O obtained at different pulsing rate (of

CH4/CO2 reaction. (Temperature = 700 oC)

Results

CEA spectra of CH4 and H2O obtained at different time on stream.

(reaction temperature =700 oC); fixed pulsing duration

Wavenumber (cm -1)

7510.6 7510.8 7511.0 7511.2 7511.4

CH4

H2O

225 min

95 min

15 min

0 min

After long reaction time, deactivation of

catalyst

Results

(1) The conversion of CO2 over La2NiO4 catalyst was

nearly 8.0 % higher than that of methane, attributable to the contribution of RWGS reaction:

CO2 + H2 CO + H2O H = + 41 kJ/mol

(2) The H2O formation in RWGS reaction increases as the temperature of the catalyst increases because of the formation of more H2.

CH4 + CO2 → 2CO + 2H2

(More than one channel for the consumption of CO2)

High Resolution Transmission electron microscopy (HRTEM) images of as-prepared La2NiO4 sol-gel-generated catalyst

HRTEM photographs of used La2NiO4 catalyst for CH4/CO2

reforming for 5 h under the condition of supersonic jet expansion; scale (a) 200 nm (b) 5 nm.

(a) (b)

Cavity enhanced absorption spectroscopy(CEAS) is an excellent technique for monitoring catalytic reaction in situ.

The reverse water-gas shift (RWGS) reaction promoted the conversion of CO2 and decreased the partial pressure of hydrogen.

With high sensitivity, it is envisaged that chemical intermediates such as HCO, OH and CH3 radicals produced in catalytic reaction could also be detected and studied.

Conclusion and Future work

Schematic Diagram of Cavity Ring-down / Raman Shifter Experimental Setup

Cavity ring down spectrum of CH4/CO2 reforming reaction at different temperature (1573 nm).

6357.0 6357.5 6358.0 6358.5 6359.0 6359.5

CO2

CO2

CO2

CO

CO2

700 oC

600 oC

500 oC

400 oC

room temp.

Sig

na

l

Wavenumber /cm-1