Surface characteristics of porous coconut shell carbon impregnated with bimetallic catalysts

IBRAHIM Yakub, KHAIRUL Anwar Mohd Said, NORSUZAILINA Mohamed Sutan, YUN Hin Taufiq-Yap and SURAHIM Mohamad

Introduction Nitrogen Oxides (NOx) from stationary sources such as

incinerators and power plants are toxic environmental pollutants

Selective catalytic reduction (SCR) is currently the most widely used method to reduce NOx emissions in power plants and automobile application

Much attention has been paid to the development of low-temperature SCR catalysts, capable of undergoing a reaction under 300 oC because; Suitable for relatively cheap and readily available precursors

such as activated carbon the exhaust contains less particulate matter that may cause

catalyst deactivation and poisoning, as well as other pollutants such as SO2 and Arsenic

carbon fiber and activated coke showed high NOx removal efficiency at low temperatures (100 – 250 oC)

Objective

To determine the potential of an SCR catalyst derived from coconut shell carbon in low-temperature SCR system using; surface chemistry characterization morphology observation

Methodology

Sample Preparation

• CSC was washed and oven dried, drenched in an equimolar mixture of copper nitrate and manganese acetate and continuously stirred for 24 hrs at room temperature

• The impregnated CSC was heat-treated under clean ambient air at 250 oC for 8 hrs and cooled to room temperature in a vacuumed desiccator

Surface chemistry

characterization

• Using H2 temperature-programmed reduction (H2-TPR), CO2 temperature-programmed desorption (CO2-TPD), NH3 temperature-programmed desorption (NH3-TPD)

Morphology observation

• Using N2 adsorption-and-desorption and scanning electron microscope (SEM)

Results & Discussion Surface Area

The BET surface area of the catalyst is larger than the carbon mainly due to the increase in external surface area after synthesis process.

This improvement is beneficial as more available sites can be introduced for the SCR reaction to take place.

Properties CSC Cu-Mn/CSC

BET surface area (m2/g) 819.2 903.3

External surface area (m2/g) 35.64 187.8

Internal surface area (m2/g) 783.5 715.5

Micro pore volume (cc/g) 39.21 35.05

Average pore diameter (Ǻ) 21.28 26.12

N2 adsorption-desorption isotherm

BET adsorption isotherms for both samples are similar, that is Type IV

hysteresis loop for CSC is Type H3 while for Cu-Mn/CSC is Type H4

the calcination process had resulted in a more uniform distribution of slit-shape pores formed by aggregates of plate-like particles

0.04 0.14 0.24 0.34 0.44 0.54 0.64 0.74 0.84 0.94220240260280300320340360380400

Adsorption

Relative Pressure, P/Po

Vol

ume,

cc/

g

Cu-Mn/CSC

CSC

Surface acidity

From the 4,599 μmol NH3 desorbed, almost 50% was allowed to detach from the basic functional groups at 674 oC while the other half at 871oC

This implies that ammonia was strongly adsorbed by the catalyst, either at the surface or at the metal oxides where it will react with NOx to form nitrogen

Surface basicity

There were 6,341 μmol CO2 desorbed form each gram of the catalyst

Most of the CO2 evolved at high temperature between 600 to 900 oC which suggests the presence of lactones

Catalyst reducibility

Copper and manganese oxides were reduced at temperature around 246 and 574 oC with at least 80% of the reduction occurred at the higher temperature

Conclusion

Coconut shell carbon utilized as SCR catalyst support showed suitable surface characteristics to be applied in low-temperature SCR system N2 adsorption-and-desorption test showed increase

in surface area and change in hysteresis loop from Type H3 to Type H4

H2-TPR showed the presence of the bimetallic catalysts which were both reduced

CO2-TPD and NH3-TPD indicated higher presence of acidic functional groups on the catalyst that is suitable for ammonia (reductant in SCR) adsorption

Acknowledgement

The authors acknowledge the Ministry of Education Malaysia for the fund RAGS/c(7)/940/2012(41) as well as Universiti Malaysia Sarawak and Universiti Putra Malaysia for the research facilities.

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