Electrochemical promotion of propylene combustion on Ag catalytic coatings

Accepted Manuscript Electrochemical promotion of propylene combustion on Ag catalytic coatings

I. Kalaitzidou, T. Cavoué, A. Boreave, L. Burel, F. Gaillard, L. Retailleau-Mevel, E.A. Baranova, M. Rieu, J.P. Viricelle, D. Horwat, P. Vernoux PII: DOI: Reference:

S1566-7367(17)30416-8 doi:10.1016/j.catcom.2017.10.005 CATCOM 5216

To appear in:

Catalysis Communications

Received date: Revised date: Accepted date:

29 June 2017 1 October 2017 3 October 2017

Please cite this article as: I. Kalaitzidou, T. Cavoué, A. Boreave, L. Burel, F. Gaillard, L. Retailleau-Mevel, E.A. Baranova, M. Rieu, J.P. Viricelle, D. Horwat, P. Vernoux , Electrochemical promotion of propylene combustion on Ag catalytic coatings. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Catcom(2017), doi:10.1016/j.catcom.2017.10.005

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Electrochemical Promotion of Propylene Combustion on Ag Catalytic Coatings I. Kalaitzidoua, T. Cavouéa, A. Boreavea, L. Burela, F. Gaillarda, L. Retailleau-Mevela, E.A. Baranovab, M. Rieuc, J.P. Viricellec, D. Horwatd and P. Vernouxa,* a

AC

CE

PT

ED

M

AN

US

CR

IP

T

Université de Lyon, Institut de Recherches sur la Catalyse et l’Environnement de Lyon, UMR 5256, CNRS, Université Claude Bernard Lyon 1, 2 avenue A. Einstein, 69626 Villeurbanne, France b Department of Chemical and Biological Engineering, Centre for Catalysis Research and Innovation, University of Ottawa, 161 Louis-Pasteur Ottawa ON K1N 6N5 Canada c École Nationale Supérieure des Mines, SPIN-EMSE, CNRS:UMR5307, LGF, F-42023 Saint-Étienne, France d Université de Lorraine, UMR CNRS 7198, Institut Jean Lamour * E-mail address: [email protected]

ACCEPTED MANUSCRIPT Abstract Catalytic and electrocatalytic tests have been carried out in a solid oxide cell for propylene combustion using two different Ag screen-printed films deposited on yttria-stabilized zirconia. Competitive adsorption between oxygen and propylene has been observed at 300°C. Catalytic performances

T

can be tailored by current application in a non-Faradaic manner. The

IP

predominant impact of current applications is to modify the reactivity of

CR

oxygen present on the Ag surface. Positive current applications enhance the propylene conversion by producing more reactive oxygen species. This

US

beneficial effect is more pronounced under lean-burn conditions where the

AN

oxygen coverage on Ag is high.

AC

CE

PT

ED

M

Keywords: Ag coatings; propylene combustion; electrochemical promotion of catalysis, Yttria-Stabilized Zirconia

ACCEPTED MANUSCRIPT 1. Introduction

Catalytic combustion as a process used for removal of hydrocarbons from automotive gas exhausts or for energy production has been widely implemented on supported PGM (Platinum Group Metals) based catalysts [1]. Since PGMs are very costly

IP

T

and rare, there is a strong need for an equally effective and less expensive catalyst. One

CR

of the solutions could be to improve catalytic performances of non-PGM catalysts by coupling catalysis with electrochemistry. The electrochemical promotion of catalysis

US

(EPOC), also named Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) effect, is a promising concept to in-operando boost catalytic processes in a

AN

reversible and controlled manner. EPOC involves electrochemical catalysts which consist

M

of a catalytic layer interfaced with an ionically conducting support. The latter serves as an electrically controlled source or sink of ionic species that activate and modulate the

ED

behavior of the catalytic surface. The migration of these charged species is controlled by

PT

the application of a potential or a current between the catalyst film and a counter electrode. Numerous surface science and electrochemical techniques have shown that

CE

EPOC is due to this electrochemically controlled migration of ions (Oδ- in case of YSZ)

AC

between the ionic conductor and the gas exposed catalytic surface [2-5]. Upon application of a small current or potential an “effective” electrochemical double layer is established on the catalyst surface, which linearly changes the catalyst-electrode work function (WF) [6,7], eΦ, of the catalyst [Eq. (1)].

Δ(eΦ) = e ΔVWR

(1)

ACCEPTED MANUSCRIPT The two parameters that are commonly used to quantify the magnitude of EPOC are the rate enhancement ratio, ρ, defined by Eq. (2) and the apparent Faradaic efficiency, Λ, given by Eq. (3) :

ρ = r/r0

T

(2)

(3)

CR

IP

Λ = Δrcatalytic/(I/2F)

where r denotes the electropromoted catalytic rate, r0 is the unpromoted rate (i.e. the

US

open-circuit catalytic rate), Δrcatalytic is the current- or potential- induced observed change in catalytic rate (in mol O/s), and I is the applied current.

AN

This study deals with the electrochemical promotion (EPOC) of propylene oxidation

M

on Ag catalytic films which, to the best of our knowledge, has never been reported in the literature. Silver, around twenty times cheaper than platinum, is a viable alterna tive

ED

solution. Ag-supported alumina catalysts have been investigated for the selective

PT

catalytic reduction of NO by propylene and large metallic Ag nanoparticles were found to be active for propylene combustion [8].

CE

EPOC of propylene combustion has been carried out in the literature but mainly on Pt

AC

catalytic films [1, 9-15]. Kaloyannis and Vayenas [9] studied the propylene oxidation on Pt films deposited on YSZ within a temperature range of 400-460o C and found that negative applied potentials enhance the rate of oxidation by up to a factor of 6 in propylene-rich conditions. The EPOC was attributed to the modification in the propylene chemisorption [9]. Similar enhancement of the propylene conversion upon negative polarizations was observed under near-stoichiometric conditions on Pt/NaSICON (Na+ conductor [11]) and Pt/β-Al2 O 3 (either Na+ [12] or K + [13] conductor) electrochemical catalysts at lower temperatures (220-300°C). In addition, with K-βAl2 O 3 , de Lucas-

ACCEPTED MANUSCRIPT Consuegra et al. [13] have evidenced the formation of stable potassium oxide/superoxide promoters on Pt, able to promote the propylene conversion in oxygen rich condition at low temperatures (190-230°C) upon positive polarizations. More recently, similar NEMCA effects were achieved at low temperatures (200°C-300°C) and lean-burn conditions by using gadolinium-doped ceria [14] or BITAVOX [15], O2- conducting solid

IP

T

electrolytes known to exhibit higher ionic conductivity at low temperature than YSZ.

CR

Furthermore, in both cases, the addition of steam in the feed did not inhibit the electrochemical activation [14,15].

US

EP studies on silver catalytic films have been reported for different reactions such as ethylene epoxidation [16-19] or toluene oxidation [20,21]. The rate of toluene oxidation

AN

was found to be significantly promoted by the negative polarization of Ag/YSZ

M

electrochemical catalysts. The magnitude of the activation depends on the toluene/oxygen ratio and the temperature (300-330°C) but can be strongly non-Faradaic (Λ values up to -

ED

39700).

PT

The aim of this study was to develop Ag-based electrochemical catalysts for low temperature propylene deep oxidation. Electrochemical catalysts (Ag/YSZ) were

CE

prepared by the screen-printing method. This latter is a flexible tool to prepare few µm

AC

thick porous films at low cost. The impact of current applications on the propylene conversion was carried out at 300°C in both oxygen-rich and stoichiometric conditions.

2. Experimental

The electrolyte was an yttria-stabilized zirconia (TOSOH powder, 99.99%; average grain size, 0.3μm), containing 8 mol% yttria, and sintered at 1350 o C for 2 h (densification higher than 98%). YSZ disks were 17 mm in diameter and 1 mm thick. Two different

ACCEPTED MANUSCRIPT commercial Ag inks (Metalon® HPS-FG32 and Metalon® HPS-090B from Novacentrix, corresponding to sample A and B, respectively) were deposited, as working (W) electrodes, via the screen-printing method on the YSZ solid electrolyte followed by a calcination at 400 or 600o C for 30 min (heating ramp of 2o C/min). A symmetrical counter-electrode (C) made of Au was deposited on the other side of the disks via the

IP

T

physical vapor deposition method (magnetron sputtering). Gold was selected because of

CR

its negligible catalytic activity in propylene oxidation, as checked via blank experiments under our experimental conditions. Both samples have a geometrical surface of around 2

US

cm2 and a Ag loading of 10 mg.cm-2 .

The quartz reactor [1] was operated under continuous flowing conditions at

AN

atmospheric pressure. The YSZ pellet was placed on a fritted quartz, 18 mm in diameter,

M

with the catalyst-electrode side facing the fritted quartz. Before catalytic tests, the electrochemical catalysts were stabilized for 12 h at 300°C under the reaction mixture.

ED

The measurement of catalytic performances was recorded during the cooling-down with a

PT

ramp of 1o C/min (Fig. S1). The impact of the partial pressure of both reactants on the CO2 production was investigated at 300o C. Since sample A was catalytically much more

CE

active than sample B (Fig. S1), all kinetic measurements were performed with an overall

AC

flow of 6 and 3 l/h for sample A and B, respectively. For electrocatalytic measurements, sample A was tested at 6 l/h in near-stoichiometric conditions (C3 H6 /O 2 : 0.1%/ 0.45%) while for sample B, the overall flow was 3 l/h in oxygen-rich conditions (C3 H6 /O2 : 0.1%/3.6%). The protocol for the transient experiments on both samples was the following: record of the OCV (Open-Circuit Voltage) catalytic activity for 1-3 h, apply negative/positive currents for 1-3 h, return to OCV for 1-3 h and then repeat the same sequence with another current.

ACCEPTED MANUSCRIPT The reactants and products were analyzed by an on- line micro gas-chromatograph (µGC-R3000, SRA) and an IR CO 2 analyzer (HORIBA VA-3000). Carbon monoxide was never detected, according to our 10 ppm lower detection limit. Working (W) and counter electrodes (C) were connected to a potentiostat- galvanostat Voltalab PGZ402 (Radiometer Analytical). Small currents, in the range -10 / +25 µA, were applied between

T

the working and counter electrodes.

IP

Fig. 1 shows SEM images (cross-views) of “fresh” samples A and B. The thickness of

CR

Ag layers is in the range 10-25 μm. Sample B was calcined at a lower temperature than

US

sample A and is thus less sintered and more porous. However, whatever the sample, the

AN

Ag grains are in the micrometer range.

ED

M

3. Results and discussion

3.1. Catalytic activity measurements under OCV

PT

The impact of the partial pressure of oxygen and propylene on the performances of

CE

both samples was investigated at 300o C. Figure 2a shows the C 3 H6 conversion and the CO2 production rate variations versus the partial pressure of oxygen for 0.1% C3 H6 (Fig.

AC

2a). On both samples, the conversion increases with PO2 , highlighting a positive apparent order. On sample A, as activity is higher, the conversion remains constant up to 2% O 2 . With respect to PC3 H6 (Fig. 2b), the conversion exhibits a maximum for low PC3 H6 values (0.05% and 0.1% on sample A and B, respectively) and then decreases showing a negative order. These experiments suggest a competitive adsorption between propylene and oxygen on silver surface (Langmuir-Hinshelwood mechanism). Therefore, high

ACCEPTED MANUSCRIPT catalytic rate can only be achieved for high coverages of oxygen (θO) and propylene (θHC) on Ag as highlighted by Eq. (4). rO = k.θO.θHC

(4)

The sharp maximum and the consequent rate decrease in Fig. 2b are due to the strongest adsorption of propylene in comparison to that of oxygen. According to the EPOC rules

IP

T

established by Vayenas et al. [22], the impact of the polarization on the catalytic

CR

performances will strongly depend on the coverage of the two reactants, and then on the operating conditions (ratios HC/O 2 ). Therefore, we have investigated the impact of the

US

applied current on the catalytic rate of sample B under lean-burn conditions (excess of oxygen, ratio O 2 /HC = 36), which corresponds to the maximum of the conversion (Fig.

AN

2b), meaning that high oxygen and propylene coverages should take place on Ag.

M

However, the catalytic rate of CO 2 production increases with the propylene concentration in the range 0.05-0.6% for 3.6% O 2 (Fig. 2b). This result shows that θ O is higher than θ HC

ED

at OCV for 0.1% C3 H6 and 3.6% O 2 . Sample A was examined near the stoichiometry

PT

where the catalyst is mainly covered by C 3 H6 and the limiting surface reactant is O 2 . For comparison, the total flow rate of the reactants was adjusted, at 6 l/h for sample A and 3

AC

samples.

CE

l/h for sample B, in order to achieve 20% propylene conversion at OCV, for both

3.2. Impact of the current application on the catalytic performances under lean-burn conditions

Catalytic activity measurements under current application were performed for sample B under lean-burn conditions. Fig. 3 corresponds to a transient effect upon successive negative and positive current applications at 300o C. Values of Faradaic efficiencies in the

ACCEPTED MANUSCRIPT range of 300 were obtained while the conversion could be tailored from 14 to 21%. Negative current applications lead to the decrease of the CO 2 production while positive current application corresponds to a pronounced increase of the catalytic performance. Positive current applications induce an increase of the cell potential, UWC. As we do not use any reference electrode, the relationship between WF and the cell potential is most

IP

T

probably not directly proportional (Eq. 4) due to the contribution of the Au CE

CR

overpotential. Nevertheless, they follow similar trends, meaning that the Ag WF (Eq. 1) increases, then decreasing the Ag electron density [6,7]. Therefore, the chemisorptive

US

bonds between Ag and propylene, which is an electron donor [22], are strengthened. On the other hand, Ag-O bonds are weakened as was evidenced by Temperature-

AN

Programmed Desorption techniques [23] because oxygen is an electron acceptor. It

M

results in an increase of the propylene coverage. This is positive for the reaction rate driven by the competitive adsorption between propylene and oxygen (Eq. 4), as under

ED

lean-burn conditions, θ O is supposed to be higher than θ HC. Furthermore, positive currents

PT

also enhance the reactivity of oxygen by producing weakly bonded oxygen species. Negative currents are expected to decrease θ HC and the reactivity of oxygen species

CE

which is detrimental to the catalytic rate, as experimentally observed.

AC

The catalytic system, especially during positive current applications (1 h each), does not reach a steady state, suggesting a slow diffusion of the ionic active species. Table 1 summarizes ρ and Λ values for both negative and positive current applications. Upon positive current applications, the rate enhancement ratio increases with the intensity of the current. This indicates that the coverage of promoting ionic species (O δ-) increases with the current, then producing more weakly bonded oxygen species coming from the gas phase. On the other hand, the magnitude of negative current application is not linked to the intensity of the current. In addition, we observe a fast and low impact of negative

ACCEPTED MANUSCRIPT current applications on the propylene conversion. This can suggest that negative currents allow a rapid removal of promoting ionic species already present on the Ag coatings at OCV as already shown on Pt films [24]. A low current of -5 µA for few min seems to be sufficient to remove all the promoting ions. The propylene conversion upon negative current applications can be considered as the intrinsic activity of Ag without any

IP

T

promoting species of the surface. These experiments point out that current applications,

CR

under lean-burn conditions, modify the propylene coverage and the reactivity of oxygen present on the surface.

US

3.3. Impact of the current application on the catalytic performances under stoichiometric

AN

conditions

M

Similar transient experiments were performed for sample A under stoichiometric conditions. Fig. 4 shows the impact of successive negative current applications on the

ED

propylene conversion and the rate of CO 2 production at 300o C. Extremely small currents

PT

(-1 / -4 µA) lead to a dramatic decrease in the catalytic rate in a profound non-Faradaic way (Λ values up to 3474 as shown in table 1). Propylene conversion can be tailored

CE

from 24.5 (OCV) to 18.8% (application of -2 μΑ). In addition, the catalytic performance

AC

of this sample after 30 h of consequent negative current applications is slightly higher, suggesting an activation of the catalytic system with time. Upon negative currents, two opposite effects are taking place as shown by Bebelis and Vayenas [25]: the increase of

θO and the decrease of the oxygen reactivity. The latter seems to be predominant, explaining the propylene conversion drop. This decay is less pronounced for -4 µA (Table 1, Fig. 4) indicating that the most negative potential (UWC = -1.7 V) results in the highest Ag WF decrease and θO increment that can partially counter-balance the

oxygen reactivity decline. Positive current applications (Fig. S2) increase the oxygen

ACCEPTED MANUSCRIPT reactivity but also decrease the oxygen coverage, which is far lower than that of propylene at OCV under these stoichiometric conditions. This results in a s light improvement of the propylene conversion but in a strongly non-Faradaic manner (Table 1). This underlines that the predominant effect of the current applications is to tailor the

T

reactivity of oxygen present on the Ag surface.

IP

4. Conclusions

CR

This study reports, for the first time, that the catalytic activity for propylene of screenprinted Ag coatings deposited onto YSZ can be tailored by current applications in a non-

US

Faradaic manner. The predominant impact of current applications is to modify the

AN

reactivity of oxygen present on the Ag surface. Positive current applications increase the propylene conversion by producing more reactive oxygen species. This beneficial effect

M

is more pronounced in an oxidizing atmosphere, where the oxygen coverage on Ag is

ED

high. This demonstrates that EPOC can enhance catalytic properties of Ag coatings for

CE

Acknowledgments

PT

the abatement of propylene in air.

This study was performed in the “EPOX” project, funded by the French National

AC

Research Agency (ANR), ANR-2015-CE07-0026.

References [1] P. Vernoux, F. Gaillard, L. Bultel, E. Siebert, M. Primet, J. Catal., 208 (2002) 412421. [2] C.G. Vayenas, Electrochemical Activation of Catalysis: Promotion, Electrochemical Promotion, and Metal-Support Interactions, Springer, 2001. [3] P. Vernoux, L. Lizarraga, M.N. Tsampas, F.M. Sapountzi, A. De Lucas-Consuegra, J.L. Valverde, S. Souentie, C.G. Vayenas, D. Tsiplakides, S. Balomenou, E.A. Baranova, Chem. Rev. 113 (2013) 8192-8260. [4] A. Katsaounis, J. Appl. Electrochem., 40 (2010) 885-902.

ACCEPTED MANUSCRIPT

AC

CE

PT

ED

M

AN

US

CR

IP

T

[5] P. Vernoux, Recent Advances in Electrochemical Promotion of Catalysis, in Catalysis Volume 29, J. Spivey and Y.-F. Han Eds., The Royal Sociey of Chemisty ISBN: 978-178262-956-6, p29-56, 2017 [6] C.A. Cavalca, G. Larsen, C.G. Vayenas, G.L. Haller, J. Phys. Chem., 97 (1993) 61156119. [7] C.G. Vayenas, S. Ladas, S. Bebelis, I.V. Yentekakis, S. Neophytides, J. Yi, C. Karavasilis, C. Pliangos, Electrochim. Acta, 39 (1994) 1849-1855. [8] K.A. Bethke, H.H. Kung, J. Catal., 172 (1997) 93-102. [9] A. Kaloyannis, C.G. Vayenas, J. Catal., 182 (1999) 37-47. [10] F. Gaillard, X. Li, M. Uray, P. Vernoux, Catal. Lett., 96 (2004) 177-183. [11] P. Vernoux, F. Gaillard, C. Lopez, E. Siebert, Solid State Ionics, 175 (2004) 609-613. [12] N.C. Filkin, M.S. Tikhov, A. Palermo, R.M. Lambert, J. Phys. Chem. A, 103 (1999) 2680. [13] A. de Lucas-Consuegra, F. Dorado, J.L. Valverde, R. Karoum, P. Vernoux, J. Catal., 251 (2007) 474-484. [14] R. Karoum, V. Roche, C. Pirovano, R.N. Vannier, A. Billard, P. Vernoux, J. Appl. Electrochem., 40 (2010) 1867-1873. [15] R. Karoum, C. Pirovano, R.N. Vannier, P. Vernoux, A. Billard, Catal. Today, 146 (2009) 359-366. [16] S. Bebelis, C.G. Vayenas, J. Catal., 138 (1992) 588-610. [17] Ch. Karavasilis, S. Bebelis, C.G. Vayenas, J. Catal. 160 (1996) 205-213. [18] Ch. Karavasilis, S. Bebelis, C.G. Vayenas, J. Catal. 160 (1996) 190-204. [19] A. Palermo, A. Husain, M.S. Tikhov, R.M. Lambert, J. Catal. 207 (2002) 331-340. [20] N. Li, F. Gaillard, Appl. Catal. B, 88 (2009) 152-159. [21] N. Li, F. Gaillard, A. Boreave, Catal. Commun., 9 (2008) 1439-1442. [22] C.G. Vayenas, S. Brosda, C. Pliangos, J. Catal., 203 (2001) 329-350. [23] D. Tsiplakides, C.G. Vayenas, J. Catal., 185 (1999) 237-251. [24] R. Karoum, A. de Lucas-Consuegra, F. Dorado, J.-L. Valverde, A. Billard, P. Vernoux, J. of Applied Electrochem., 38 (2008) 1083-1088. [25] S. Bebelis, C.G. Vayenas, J. Catal., 138 (1992) 570-587.

ACCEPTED MANUSCRIPT Figure captions

Fig. 1. SEM images (cross-views) of the “fresh” Ag coatings interfaced on YSZ. A) sample A, calcined at 600 o C and B) sample B calcined at 400 o C (right). Fig. 2. CO2 production rate (solid lines) and propylene conversion (dotted lines)

IP

T

variations at OCV versus a) P O2 at PC3 H6 =0.1% and b) PC3 H6 at PO2 =3.6% for samples A

CR

(6 l/h) and B (3 l/h). T = 300o C.

Fig. 3. Transient effect of applied currents (Sample B) on UWC as well as on the catalytic

US

rate of CO 2 production and on C3 H6 conversion. T = 300o C. PC3 H6 = 0.1%, PO2 = 3.6%, total flow = 3 l/h.

AN

Fig. 4. Transient effect of applied currents (Sample A) on UWC as well as on the catalytic

M

rate of CO 2 production and on C 3 H6 conversion. T = 300o C. PC3 H6 = 0.1%, PO2 = 0.45%, total flow= 6 l/h.

AC

CE

PT

ED

Table captions

AC

CE

PT

ED

M

AN

US

CR

IP

T

ACCEPTED MANUSCRIPT

AC

CE

PT

ED

M

AN

US

CR

IP

T

ACCEPTED MANUSCRIPT

AC

CE

PT

ED

M

AN

US

CR

IP

T

ACCEPTED MANUSCRIPT

AC

CE

PT

ED

M

AN

US

CR

IP

T

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

AC

CE

PT

ED

M

AN

US

CR

IP

T

Graphical abstract

ACCEPTED MANUSCRIPT Table 1: Rate enhancement ratio and apparent Faradaic efficiency values for samples B (lean-burn conditions) and A (stoichiometric conditions).

ED PT CE AC

IP CR

Λ 2441 3474 1960 1284 571

US

ρ 0.92 0.78 0.81 0.84 1.03

AN

Λ 289 74 296 214 177 154 137

M

Current Applied / μA -1 -2 -3 -4 2

ρ 0.86 0.92 1.15 1.22 1.27 1.31 1.34 Sample A

T

Sample B Current Applied / μA -5 -10 5 10 15 20 25

ACCEPTED MANUSCRIPT Highlights  Ag coatings were screen-printed on YSZ, an O 2- ionic conductor 

Catalytic performances for propylene combustion can be electrochemically tailored Current applications mainly modify the reactivity of oxygen on Ag



EPOC can enhance Ag catalytic performance for propylene abatement in air

AC

CE

PT

ED

M

AN

US

CR

IP

T

