83

Topics in Catalysis Vols. 42–43, May 2007 ( 2007) DOI: 10.1007/s11244-007-0156-4

A kinetic study of NOx reduction over Pt/SiO2 model catalysts with hydrogen as the reducing agent Anna Lindholma, Neal W. Currierb, Aleksey Yezeretsb, and Louise Olssona,* a

Competence Centre for Catalysis, Chalmers University of Technology, SE-412 96 Go¨teborg, Sweden b Cummins Inc., 1900 McKinley Ave, MC 50183, Columbus, IN, 47201 USA

Flow reactor experiments and kinetic modeling have been performed in order to study the mechanism and kinetics of NOx reduction over Pt/SiO2 catalysts with hydrogen as the reducing agent. The experimental results from NO oxidation and reduction cycles showed that N2O and NH3 are formed when NOx is reduced with H2. The NH3 formation depends on the H2 concentration and the selectivity to NH3 and N2O is temperature dependent. A previous model has been used to simulate NO oxidation and a mechanism for NOx reduction is proposed, which describes the formation/consumption of N2, H2O, NO, NO2, N2O, NH3, O2 and H2. A good agreement was found between the performed experiments and the model. KEY WORDS: NOx reduction; hydrogen; Pt/SiO2; kinetic modeling; NH3; N2O; N2.

1. Introduction The NOx storage technology (also referred to as lean NOx traps, LNT) is a method to reduce nitrogen oxides in lean exhausts [1,2]. In this technique NOx is stored in the catalyst during lean conditions (oxygen excess). To regenerate the catalyst, fuel rich exhausts are used for a short period of time where NOx is released and reduced. A typical LNT catalyst consists of: precious metals, such as Pt or Pd and Rh, a storage component, typically barium, and a high surface area support, such as c-alumina. It has been shown that hydrogen is very effective at regenerating LNTs from stored NOx [3]. There are several studies of NO reduction with hydrogen over platinum single crystals [4,5] as well as over supported platinum catalysts [6,7]. Earlier studies of NOx storage catalysts have focused on details of the storage period and detailed kinetic models have been constructed by Olsson et al. [1,2]. However, the reactions occurring during the reduction phase have not yet been fully resolved. The objective of this work is to investigate the reduction of NOx over Pt/SiO2 model catalysts by means of flow reactor experiments and detailed kinetic modeling. In order to isolate the reduction on Pt without interference of released NOx from storage materials and support materials, we have chosen to study Pt/SiO2. Furthermore, we have focused on the reduction with hydrogen on coated monoliths. Since the LNT technology is highly time-dependent, we have also studied transient experiments. This model is a part of a complete

* To whom correspondence should be addressed. E-mail: [email protected]

NOx storage/reduction model with hydrogen as the reducing agent.

2. Experimental A Pt/SiO2 monolith catalyst with a washcoat weight of 1054 mg, containing 3.0 wt-% Pt, was used in this study. The sample was 30 mm long, 21 mm in diameter and had a cell density of 400 cpsi. The specific surface area of the sample, according to the BET method, was 133 m2/gwashcoat and the platinum dispersion, determined by N2O dissociation [8], was 16%. Incipient wetness impregnation method was used [9], with Pt(NH3)4(OH)2 as platinum precursor. Flow reactor experiments were conducted, with a total flow rate of 3500 ml/min, which corresponds to a space velocity of 20210 h)1. Argon was used as carrier gas in all measurements. The outlet gases were analyzed with a chemiluminiscence NOx detector (CLD 700) and with a gas FTIR (Bio-Rad FTS 3000 Excalibur Spectrometer with a Specac Sirocco series heatable gas cell, P/N 24102, with a 2 m pathlength and a volume of 0.19 l). NO oxidation and reduction cycles were conducted at 100
C, 200
C and 300
C. The lean periods were 4 min long and the rich periods were 1 minute long. The composition of the lean gas mixture was 300 ppm NO and 8% O2 and the rich gas mixture contained 300 ppm NO and either 2000 ppm H2 or 8000 ppm H2. Additionally, NO2 dissociation and reduction cycles at 300
C were performed, where the composition of the lean gas mixture was 300 ppm NO2 and 8% O2 and the composition of the rich gas mixture was 300 ppm NO2 and 8000 ppm H2. In all measurements the sample was pretreated at 500
C with 10 min of 8% O2 in Ar 1022-5528/07/0500-0083/0  2007 Springer Science+Business Media, LLC

84

A. Lindholm et al./A kinetic study of NOx reduction

followed by 5 min of 100% Ar and thereafter 10 min of 1.8% H2.

3. Kinetic model The kinetic model is a mean field model where the monolith is described as a series of continuously stirred tank reactors. In the calculations presented in this work 10 tanks in series were used. The rate constant is described by the Arrhenius expression. In order to decrease the number of free parameters in the model the pre-exponential factors for adsorption were determined by using kinetic gas theory, for details see [1,2]. The mass transport is described by the film model and the correlation for the Sherwood number is taken from [10].

Figure 1 shows measured and calculated outlet steady state concentrations of NO and NO2 (left panel) for NO oxidation over Pt/SiO2 (300 ppm NO and 8% O2) and the calculated mean coverages (right panel) at 100
C, 200
C and 300
C. The NO oxidation capacity is well described by the model at all temperatures. Furthermore, the ability for platinum to dissociate NO2 to NO can be described by the model and this is also presented in Figure 1. The model predicts a high oxygen coverage at 200
C and 300
C which is reasonable since the concentration of oxygen in the experiments is high (8% O2). At 100
C there is a higher coverage of NO than of oxygen on the surface. The reason for this is a combination of the low NO oxidation capacity, the higher sticking coefficient of NO compared to O2 and the low NO desorption rate at 100
C. 4.2. NOx reduction on Pt/SiO2

4. Results and discussion 4.1. NO oxidation on Pt/SiO2 The model describing NO oxidation over Pt in this work is the model previously developed by Olsson et al. [2] for Pt/Al2O3, where the kinetics is based on a Langmuir-Hinshelwood mechanism. Only 2 parameters out of 18 had to be fitted in order to describe the NO oxidation over Pt supported by silica. Three parameters were calculated from thermodynamic constraints and the remaining 13 parameters were taken from [2]. Olsson et al. used an activation energy of 115.5 kJ/mol for NO desorption. The activation energy for NO desorption in this work was fitted to 106.5 kJ/mol. Also the activation energy for O2 adsorption used in this work was slightly lower than the activation energy used by Olsson et al. (20.4 kJ/mol compared to 30.4 kJ/mol). The support material and the used Pt precursor can affect the activity of Pt. However, only small modifications of two parameters were needed, as described. Table 1 presents the mechanism, the reaction rates and the kinetic parameters that are used for NO oxidation in this work.

The NOx reduction mechanism and the kinetic parameters used in this work are presented in Tables 2–5. Hydrogen was used as a reducing agent and the adsorption and desorption of hydrogen are described by reaction 9 and 10. The sticking coefficient for hydrogen (S = 0.046) was taken from Ljungstro¨m et al. [11] and the activation energy for adsorption was assumed to be 0 kJ/mol. We used the activation energy for hydrogen desorption that Lu et al. [12] proposed (96.2 kJ/mol), which also is in the range that Savargonkar observed (83–110 kJ/mol) [13]. Reaction 11 and 12 describe the dissociation of NO and the formation of NO from nitrogen and oxygen adsorbed on platinum. Montreuil et al. [14] used different kinetics depending on the k-value when modeling three-way catalysts, assuming that platinum behaves differently in lean and rich environment. In our model we took that into account by letting the activation energy for NO dissociation be higher when oxygen is present on the platinum surface. This will prevent NO from dissociating during the lean period and the

Table 1 Mechanism, reaction rates and kinetic parameters for NO oxidation Nr. 1. 2. 3. 4. 5. 6. 7. 8. a b c d e

Reaction r1

NOðgÞ þ Pt ! NO
Pt r2 NO
Pt ! NOðgÞ þ Pt r3 O2ðgÞ þ 2Pt ! 2O
Pt r4 2O
Pt ! O2ðgÞ þ 2Pt r5 NO
Pt þ O
Pt ! NO2
Pt þ Pt r6 NO2
Pt þ Pt ! NO
Pt þ O
Pt r7 NO2
Pt ! NO2ðgÞ þ Pt r8 NO2ðgÞ þ Pt ! NO2
Pt

Reaction rate r1 r2 r3 r4 r5 r6 r7 r8

¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼

k1  cNOðgÞ  hv;Pt k2  hPt
NO k3  cO2 ðgÞ  h2v;Pt k4  h2Pt
O k5  hPt
NO  hPt
O k6  hPt
NO2  hv;Pt k7  hPt
NO2 k8  cNO2 ðgÞ  hv;Pt

Preexp. factor (A) 3,a

5.3 · 10 1.0 · 1016,b 1.3 · 102,a 1.0 · 1015,b 1.0 · 1013,b 1.1 · 1012,b,d 1.0 · 1016,b 4.8 · 103,a

Ref.

Ea [kJ/mol]

Ref.

[2] [2] [2] [2] [2] [2] [2] [2]

0 108.5c 20.4c 199.4d,e 101.2 59.5d 97.9e 0

[2]

Unit: m3/(s kg washcoat) Unit: s)1 Parameter fitted in this work. Calculated from thermodynamic restrictions [2]. The activation energy is dependent on the oxygen coverage, i.e. Ei ðhÞ ¼ Ei ð0Þ  ð1
ai  hPt
O Þ. a4 ¼ 0:116 and a7 ¼ 0:118

[2] [2] [2] [2] [2]

85

A. Lindholm et al./A kinetic study of NOx reduction

NO

0.8

200

Coverage

Concentration (ppm)

NO2 in the feed 250

NO exp. NO calc. NO2 exp. NO2 calc.

150 100

NO2

50

150

0.4

0.2

NO2 in the feed 100

Pt-O Pt-NO

0.6

200

250

0.0 300

100

150

200

250

300

Temperature (°C)

Temperature (°C)

Figure 1. Left panel: Measured (dashed lines) and calculated (solid lines) stationary outlet concentrations of NO and NO2 for NO oxidation (300 ppm NO and 8% O2) at three temperatures. Measured (n) and calculated (h) stationary outlet concentrations of NO and NO2 for NO2 dissociation (300 ppm NO2 and 8% O2). Right panel: Calculated mean coverages for NO oxidation.

reduction reactions will therefore not occur in oxygen excess. Nitrogen is the desired product for NOx reduction and different mechanisms for the formation of N2 have been proposed in the literature [5,7,15]. Mechanisms where hydrogen reacts directly with NO have also

been proposed [16]. We have chosen to describe the formation of N2 by recombination of nitrogen atoms [15], see reaction 13. Reaction 14 describes the formation of H2O from oxygen and hydrogen. When the hydrogen concentration is increased the rate of reaction

Table 2 Mechanism, reaction rates and kinetic parameters for NOx reduction Nr.

Reaction

Reaction rate

Pre-exp. factor (A)

Ref.

Ea [kJ/mol]

Ref.

9. 10. 11. 12. 13. 14. 15. 16.

H2ðgÞ þ 2Pt ! 2H
Pt r10 2H
Pt ! H2ðgÞ þ 2Pt r11 NO
Pt þ Pt ! N
Pt þ O
Pt r12 N
Pt þ O
Pt ! NO
Pt þ Pt r13 2N
Pt ! N2ðgÞ þ 2Pt r14 O
Pt þ 2H
Pt ! H2 O
Pt þ 2Pt r15 H2 OðgÞ þ Pt ! H2 O
Pt r16 H2 O
Pt ! H2 OðgÞ þ Pt

r9 ¼ k9  cH2 ðgÞ  h2v;Pt r10 ¼ k10  h2Pt
H r11 ¼ k11  hPt
NO  hv;Pt r12 ¼ k12  hPt
N  hPt
O r13 ¼ k13  h2Pt
N r14 ¼ k14  hPt
O  h2Pt
H r15 ¼ k15  cH2 OðgÞ  hv;Pt r16 ¼ k16  hPt
H2 O

9.1 · 102,a 1 · 1015,b 3.9 · 1016,b,c 1 · 1013,b 1 · 1013,b 2.2 · 1017,b,c 5.3 · 103,a 1 · 1016,b

[11] Held const.

0 96.2 93.0c 68.2c 79.49 54.4 0 65

Held const. [12]

a b c

r9

Held const. Held const. [18] Held const.

[15] [17] Held const. [18]

Unit: m3/(s kg washcoat) Unit: s)1 Parameter fitted in this work.

Table 3 Mechanism, reaction rates and kinetic parameters for formation, adsorption and desorption of NH3 Nr. 17. 18. 19. a b c

Reaction

Reaction rate

r17

N
Pt þ 3H
Pt ! NH3
Pt þ 3Pt r18 NH3ðgÞ þ Pt ! NH3
Pt r19 NH3
Pt ! NH3ðgÞ þ Pt

r17 ¼ k17  hPt
N  hPt
H r18 ¼ k18  cNH3 ðgÞ  hv;Pt r19 ¼ k19  hPt
NH3

Pre-exp. factor (A)

Ref.

11,b,c

9.2 · 10 7.1 · 103,a 2.0 · 1016,b,c

Ea [kJ/mol]

Ref.

c

[21]

78.63 0 75.3

Held const. [22]

Unit: m3/(s kg washcoat) Unit: s)1 Parameter fitted in this work.

Table 4 Mechanism, reaction rates and kinetic parameters for N2O formation Nr.

Reaction

Reaction rate

Pre-exp. factor (A)

Ref.

Ea [kJ/mol]

20.

2NO
Pt ! N2 OðgÞ þ O
Pt þ Pt

r20 ¼ k20  h2Pt
NO

1.0 · 1013,a

Held const.

74.97b

a b

r20

Unit: s)1 Parameter fitted in this work

86

A. Lindholm et al./A kinetic study of NOx reduction Table 5 Mechanism, reaction rates and kinetic parameters for the reaction steps including SiO2

Nr.

Reaction H
Pt þ SiO2 ! Pt þ SiO2
H r22 Pt þ SiO2
H ! H
Pt þ SiO2 r23 4SiO2
H þ 2NO
Pt ! N2 þ 2H2 O þ 2Pt þ 4SiO2

21. 22. 23. a b

Reaction rate

r21

r21 ¼ k21  hPt
H  hv;SiO2 r22 ¼ k22  hSiO2
H  hv;Pt r23 ¼ k23  hSiO2
H  hPt
NO

Pre-exp. factor (A) 17,a,b

3.0 · 10 2.7 · 1010,a,b 1.1 · 1011,a,b

Ea [kJ/mol] 90b 45b 105b

Unit: mol/ (s · kg of washcoat) Parameter fitted in this work

14 is increased, resulting in an increased rate of the NO dissociation and thereby a more effective NOx reduction. Reaction 15 and 16 describe the water adsorption and desorption, respectively. Some of the pre-exponential factors for the above mentioned reactions are kept constant in order to decrease the number of free parameters in the modeling. The pre-exponential factor for hydrogen desorption was fixed at 1015 s)1, reaction 12 and 13 at 1013 s)1 and the pre-exponential factor for reaction 16 was set to 1016 s)1. Adsorption reactions are usually non-activated and the activation energies for hydrogen adsorption and water adsorption were therefore set to 0 kJ/mol. Fitted parameters are A11, Ea11, Ea12 and A14. A significant amount of ammonia is formed over platinum during the rich period when using 2000 ppm H2 and 8000 ppm H2. This is shown in Figure 2 where the measured stationary ammonia concentrations at 100, 200 and 300
C are presented for both hydrogen concentrations. There is experimental evidence that NHx intermediates exist on platinum single–crystal surfaces [4,19,20]. However, we have chosen to describe the NH3 formation as one irreversible global reaction step in order to decrease the number of reaction steps. Table 3 presents the mechanism, reaction rates and kinetic

300

Concentration (ppm)

250

Calc. NH3 (8000 ppm H2)

200

Exp. NH3 (8000 ppm H2)

Calc. Exp.

150

Calc. NH3

(NO2 in the feed)

(2000 ppm H2)

100

Exp. NH3 (2000 ppm H2)

50

0 100

150

200

250

300

Temperature (°C) Figure 2. Measured (solid) and calculated (dashed) stationary outlet concentrations of NH3 for NOx reduction with 300 ppm NO and 8000 ppm H2 (or 2000 ppm H2) at three temperatures. Measured (n) and calculated (h) stationary outlet concentrations of NH3 for NOx reduction with 300 ppm NO2 and 8000 ppm H2. The reactions used in the modeling are described in Table 2–5.

parameters for formation (r17), adsorption (r18) and desorption (r19) of NH3. Bradley et al. measured the sticking probability versus ammonia coverage over Pt(100) and reported that sticking is 0.9 for coverages lower than 0.35 (adsorbed NH3 divided by total amount of Pt sites). Furthermore, their results indicated that the adsorption is non-activated (Ea = 0 kJ/mol) [21]. We have chosen to apply these values for the NH3 adsorption parameters used in our model. The activation energy for desorption of ammonia is taken from Gohndrone [22] and set to 75.3. Fitted parameters are A17, Ea17 and A19. Nitrous oxide is formed over platinum at low temperatures during reduction of NOx with hydrogen. Different mechanisms for N2O formation have been proposed in the literature. Burch et al. performed DFT calculations which supported the formation of N2O from a (NO)2 dimer species [23,24]. We have therefore chosen to formulate the N2O formation as illustrated in Table 4. The pre-exponential factor was set to 1013 s)1 and the activation energy was fitted. Experiments performed in this study showed that there is a delay in the ammonia signal when using a lower amount of hydrogen in the rich period. In order to describe this feature in the model we have added a reversible hydrogen spillover step (r21 and r22), where adsorbed hydrogen on platinum can spill over to the silica support and reversibly move back to the platinum sites. Hydrogen spillover to the support has previously been reported in the literature by Arai et al. [25] and Miller et al. [26]. It is also suggested in the literature, based both on experiment and simulations that surface spillover of NOx between Pt sites and Barium sites occurs in lean NOx traps [2]. Experiments where NOx desorption from Ba/Al2O3 and Pt/Ba/Al2O3 was compared showed that the addition of platinum resulted in an increased desorption of NOx [2]. Significant amounts of the stored NOx was released at a lower temperature, thus we suggest that NOx spill-over can occur over quite large distances. Since hydrogen is a smaller molecule than NOx it is reasonable to believe that also hydrogen spillover can occur in the same way. Further, a global reaction step (r23) describing how hydrogen on silica sites close to platinum sites can react with adsorbed NO on platinum and form N2, has been added to the model. The reactions and parameters describing the mechanism including silica are presented in Table 5. All of the

87

A. Lindholm et al./A kinetic study of NOx reduction

(14 ppm, see Figure 4) and the rest is assumed to be nitrogen. Figure 4 shows the N2O concentrations for experiments and simulations presented in Figure 3. Also the measured and calculated values at 200
C are presented here. It can be seen that the selectivity to N2O decreases with temperature and at 200
C and 300
C only a few ppm of N2O is produced. Results from NO oxidation and reduction cycles at 100
C and 200
C, with a lower hydrogen concentration in the rich period, are presented in Figure 5. The lean gas mixture consists of 300 ppm NO and 8% O2 and the rich gas mixture of 300 ppm NO and 2000 ppm H2. The results show that it takes longer time for NOx to be

200

200 °C 100

100 °C

0 160

180

200

220

300

NOx

NO

200 150

NH3

100

NO2

50

280

300

Rich

Lean

Rich

250

260

Figure 4. Measured (solid) and calculated (dashed) outlet concentrations of N2O for NO oxidation and NOx reduction cycles at 100
C, 200
C and 300
C. The inflow concentrations are 300 ppm NO and 8% O2 during lean and 300 ppm NO and 8000 ppm H2 during rich. The reactions used in the modeling are described in Table 1–5.

350

Lean

240

Time (s)

Concentration (ppm)

Concentration (ppm)

300

300 °C

350

300

NOx

250 200

NH3

NO2

150

NO

100 50 0

0 160

180

200

220

240

260

280

300

160

180

200

220

240

260

H-SiO2

0.8

0.8

O-Pt

O-Pt N-Pt

Coverage

NO-Pt

0.4

300

H-SiO2

H-Pt 0.6

280

Time (s)

Time (s)

Coverage

Rich

Lean

Concentration (ppm)

parameters, together with the number of SiO2 sites, were fitted. The calculated number of SiO2 sites was 2.5 mol/ kg of washcoat, which corresponds to 15.5% of the total amount of silica applied on the catalyst. Figure 2 shows the experimental and calculated stationary NH3 concentrations as a function of temperature for two different hydrogen concentrations (2000 ppm H2 and 8000 ppm H2) using the kinetic model described in Tables 2–5. A simulation with 300 ppm NO2 and 8000 ppm H2 is also presented. The NH3 formation is lower at 100
C than at 200
C and 300
C. At the higher temperatures almost all incoming NOx is converted into ammonia. Furthermore, the experiment with 2000 ppm H2 show a lower NH3 concentration than the measurement with the higher hydrogen concentration. Results from experiments and simulations of NO oxidation and reduction cycles at 100
C and 300
C are presented in Figure 3. The lean gas mixture contained 300 ppm NO and 8% O2 and the composition of the rich gas mixture was 300 ppm NO and 8000 ppm H2. The upper panels show the NO, NO2 and NH3 outlet concentrations and the lower panels show the calculated mean coverages. It can be seen that hydrogen completely reduces NOx and that the reduction occurs very fast. Ammonia starts to form as soon as the NOx concentration is low enough (below 20 ppm). At 300
C almost all NOx is converted into NH3 (282 ppm NH3 is formed from 300 ppm NOx) and the remaining is assumed to be nitrogen (not measured in the experiments). The selectivity towards ammonia is lower at 100
C and only 230 ppm NH3 is formed from 300 ppm NOx. At this low temperature also N2O is formed

0.6

0.4 H-Pt 0.2

0.2

0.0

0.0 160

180

200

220

240

Time (s)

260

280

300

320

160

180

200

220

240

260

280

300

Time (s)

Figure 3. Upper panels: Measured (solid) and calculated (dashed) outlet concentrations of NO, NO2 and NH3 for NO oxidation and NOx reduction cycles at 100
C (left) and 300
C (right). The inflow concentrations are 300 ppm NO and 8% O2 during lean and 300 ppm NO and 8000 ppm H2 during rich. Lower panels: Calculated mean coverages. The reactions used in the modeling are described in Table 1–5.

88

A. Lindholm et al./A kinetic study of NOx reduction 350

Lean

Concentration (ppm)

Concentration (ppm)

350

Rich

Lean 300 250

NO

NOx

200

NH3

150 100

NO2

50

NOx

250 200

NO2

NH3

150

NO

100 50 0

0 160

180

200

220

240

260

280

300

160

180

200

Time (s)

220

240

260

280

300

Time (s)

0.8

0.8

0.6

0.4

O-Pt N-Pt

0.2

H-Pt H-SiO2

Coverage

NO-Pt

Coverage

Rich

300

O-Pt 0.6

0.4

H-SiO2 0.2

0.0

H-Pt

0.0 160

180

200

220

240

260

280

300

160

180

Time (s)

200

220

240

260

280

300

Time (s)

Figure 5. Upper panels: Measured (solid) and calculated (dashed) outlet concentrations of NO, NO2 and NH3 for NO oxidation and NOx reduction cycles at 100
C (left) and 200
C (right). The inflow concentrations are 300 ppm NO and 8% O2 during lean and 300 ppm NO and 2000 ppm H2 during rich. Lower panels: Calculated mean coverages. The reactions used in the modeling are described in Table 1–5.

reduced when 2000 ppm H2 is used than when 8000 ppm H2 is used. It is also clear that there is a longer delay before the NH3 signal is detectable for the lower hydrogen concentration compared to the higher concentration. This is described by the reversible hydrogen spillover from platinum to silica, as mentioned before. The delay is well described by the model at 100
C. However, at 200
C the delay predicted by the model is shorter compared to the experiment. The plots of the mean coverages illustrate that it takes longer time for the surface to change from lean conditions to rich conditions, when a lower concentration of reducing agent is used.

5. Conclusions In this work we present a mean field kinetic model, describing NO oxidation and NOx reduction over Pt/SiO2 catalysts with hydrogen as the reducing agent. The model consists of two parts, one part describing NO oxidation and the other describing NOx reduction with hydrogen. Hydrogen was found to effectively reduce NOx over the Pt/SiO2 catalyst and experimental results showed that a significant amount of ammonia was formed in the examined temperature range. The selectivity towards ammonia formation is temperature dependent i.e. higher temperatures favor the NH3 production. In addition, nitrous oxide was produced and the formation was favored at lower temperatures. The model describes the formation/consumption of N2, H2O, NO, NO2, N2O, NH3, O2 and H2. A good agreement was found between the performed experiments and the model.

Acknowledgments The authors would like to thank Cummins Inc. for the financial support.

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