and utilizing reduction promoters leads to improved conversion and - - PowerPoint PPT Presentation

LC LCCP Laboratory of Catalysis and Catalytic Processes

Mohammad Mehrbod Mechanical Engineering Program, Mechanical Engineering Dept., UTSA Michela Martinelli, Burtron H. Davis Center for Applied Energy Research, University of Kentucky Donald C. Cronauer, A. Jeremy Kropf, Christopher L. Marshall Advanced Photon Source, Argonne National Laboratory Gary Jacobs Chemical Engineering Program – Dept. of Biomedical Engineering/ Dept.

• f Mechanical Engineering, UTSA

March 18, 2017

Fischer-Tropsch synthesis: foregoing calcination and utilizing reduction promoters leads to improved conversion and selectivity with Co/silica

LC LCCP Laboratory of Catalysis and Catalytic Processes

Introduction

Natural Gas Coal Biomass SYNGAS CO and H2

Hydrogen

Oxygenate Synthesis CO + 2H2 → CH3OH

FT Catalyst

Fischer-Tropsch Synthesis CO + 2H2 → -[CH2]n- + H2O Diesel Jet Fuel Waxes Lubricants PEM Fuel Cells/SOFC Portable Power Water-gas Shift / Preferential Oxidation CO + H2O → H2 + CO2 CO + 1/2O2 → CO2 Methanol, Ethanol Gasification C + H2O → CO + H2 Steam Reforming / Partial Oxidation CH4 + H2O → CO + 3H2 CH4 + 1/2O2 → CO + 2H2

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LC LCCP Laboratory of Catalysis and Catalytic Processes

Introduction

Catalyst support and promoter:

 Cobalt often supported on metal oxide carriers like alumina or titania.

We consider 3 aspect: Activity (CO conversion per gram of cat.) Product Selectivity Stability

Past efforts1,2 showed that direct reduction of cobalt nitrate led to small, difficult-to-reduce Co species. We revisit the possibility of direct cobalt nitrate reduction, but utilize promoters to facilitate activation of the difficult-to-reduce Co species.

Pt Re Ru Ag Promoter

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Co/SiO2 Co/Al2O3 Co/TiO2 Problem: The weak interaction between SiO2 and cobalt oxides on calcined catalysts leads to agglomerated Co0 after

• activation. Productivity is lower.
• 1. B.H. Davis, E. Iglesia, DOE Quarterly Report #8, July-September 2000, Technology Development for Iron and Cobalt Fischer-Tropsch Catalysts, Contract

DE-FC26-98FT40308, Final Report, June, 30 2004.

• 2. Li, J.; Jacobs, G.; Das, T.K.; Zhang Y.; Davis, B.H., Applied Catalysis A: General 236 (2002) 67-76.

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Experimental Catalyst preparation

12% wt. Co/SiO2

PQ Co. CS-2133, dried 80˚C to 100˚C

Promoted Unpromoted Calcined at 350 °C Uncalcined Calcined at 350 °C Uncalciend

To prepare 0.5 wt.% (calcined basis) Pt promoted catalysts, tetraamineplatinum (II) nitrate was added by IWI to the dried Co(NO3)2/silica parent batch, and the material was dried again in the rotary evaporator.

Calcined 12%Co/SiO2 0.5%Pt- 12%Co/SiO2 0.276%Ag- 12%Co/SiO2 0.477%Re- 12%Co/SiO2 0.259%Ru- 12%Co/SiO2 Uncalcined 12%Co/SiO2 0.5%Pt- 12%Co/SiO2 0.276%Ag- 12%Co/SiO2 0.477%Re- 12%Co/SiO2 0.259%Ru- 12%Co/SiO2

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• BET surface area and porosity measurements

BET surface area and porosity characteristics were measured using a Micromeritics 3-Flex system.

• Temperature programmed reduction

TPR profiles of calcined catalysts were recorded using a Zeton- Altamira AMI-200 unit equipped with a thermal conductivity detector (TCD).

• Hydrogen chemisorption and percentage reduction by pulse

reoxidation Hydrogen chemisorption was conducted by using temperature programmed desorption (TPD), also measured with the Zeton- Altamira AMI-200 instrument

• TPR-EXAFS/ TPR-XANES spectroscopies

In-situ H2-TPR XAFS studies were performed at the Materials Research Collaborative Access Team (MR-CAT) beamline at the Advanced Photon Source, Argonne National Laboratory

• Catalytic activity

FTS reaction tests were conducted using a 1 L CSTR equipped with a magnetically driven stirrer with turbine impeller

Experimental

LC LCCP Laboratory of Catalysis and Catalytic Processes

BET surface area and porosity measurements Results

Sample Thermal treatment As (BET) (m2/g) Vp (BJH Des) (cm3/g) Average Dp (BJH Des) (nm) SiO2 349 2.68 24.3 12%Co/SiO2 uncalcined 163 0.79 14.4 reduced 272 1.11 14.2 air calcined 278 1.16 14.6 air calcined/reduced 276 1.16 14.8 0.5%Pt-12%Co/SiO2 Uncalcined 139 0.67 13.4 Reduced 256 0.99 13.5 air calcined 275 1.00 13.6 air calcined/reduced 258 1.03 13.9 0.236%Ag- 12%Co/SiO2 Uncalcined 151 0.67 13.2 Reduced 263 0.96 13.0 0.259%Ru- 12%Co/SiO2 Uncalcined 155 0.71 13.7 Reduced 277 0.89 13.9 0.477%Re- 12%Co/SiO2 Uncalcined 156 0.73 13.9 Reduced 273 1.00 13.5

BET surface area and BJH porosity measurements.

If the support is the main contributor to the area, then after adding 12.3 wt. % Co and assuming no pore blocking, the specific surface area should decrease to 291 m2/g for the air calcined Co catalyst and 225 m2/g for the uncalcined catalyst.

2-Theta (°)

10 20 30 40 50 60 70 80 90

Intensity (a.u.) (a) (b) (c)

XRD analysis of the catalysts.

air calcined 12%Co/SiO2 uncalcined 12%Co/SiO2 uncalcined 0.5%Pt-12%Co/SiO2

LC LCCP Laboratory of Catalysis and Catalytic Processes

Result

Cobalt Reducibility:

TPR profiles of uncalcined and calcined catalysts

12%Co/SiO2 calcined 0.5%Pt-12%Co/SiO2 calcined 12%Co/SiO2 uncalcined 0.5%Pt-12%Co/SiO2 uncalcined 0.276%Ag-12%Co/SiO2 calcined 0.259%Ru-12%Co/SiO2 uncalcined 0.477%Re-12%Co/SiO2 uncalcined

Figure reveals that the air calcined catalyst reduced at a relatively low temperature Co3O4 + H2 = 3CoO + H2O 3CoO + 3H2 = 3Co0 + 3H2O For uncalcined, promoter addition did not shift the peak for nitrate decomposition (black) but did shift the peaks for reduction of cobalt

• xides (red) derived from nitrate

decomposition.

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Results

0.5%Pt-12%Co/SiO2 calcined

Cobalt Reducibility:

H2-TPR Mass Spectrometry

 The hydrogen has two consumption peaks, associated with H2O production for the calcined sample These peaks are due to the two reduction steps from Co3O4 to Co involving CoO as an intermediate, as previously discussed There is a small peak on H2O profile at temperatures lower than 100°C. This is probably due to some adsorbed water on the catalyst.

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Results

Cobalt Reducibility:

12%Co/SiO2 uncalcined TPR Mass Spectrometry

At temperatures lower than 180 °C, there are at least six major events, whereby: 1- The water signal increases

from ambient temperature until a maximum, which is reached at 110°C 1 2- Cobalt nitrate thermal decomposition without involvement of H2 occurs between 110 and 180 °C 2 3- between 180 °C and 230 °C, reductive decomposition of cobalt nitrate occurs, with continuing evolution of NO2 and H2O, including uptake by hydrogen 3 4 4- Between 200°C and 250°C, formation of NO indicates

• xidation of CoOx species

formed from the decomposition

• f cobalt nitrate by the liberated

NO2 to the spinel structure Co3O4 5 5- Between 230 °C and 300 °C, there is an uptake of hydrogen and H2O evolution without NOX formation due to reduction of the suggested spinel (e.g., Co3O4) to CoO 6 6- Between 300 °C and 750 °C, there is a series of hydrogen uptakes with corresponding evolution of H2O peaks, these are assigned to reduction of CoO species

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Results

0.5%Pt-12%Co/SiO2 ucalcined 0.477%Re-12%Co/SiO2 uncalcined 0.276%Ag-12%Co/SiO2 uncalcined 0.259%Ru-12%Co/SiO2 uncalcined

The ranking of promoter effectiveness for CoO reduction from TPR-MS is: Pt > Re > Ru > Ag > unpromoted

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Results

TPR XANES

This calcined catalyst starts with a line shape resembling the cobalt oxide spinel structure of Co3O4, with conversion to CoO being achieved below 250 °C. Next, because of the larger weakly interacting Co clusters, Co0 metal is rapidly formed by ~300 °C (final dark blue spectrum to first green spectrum for CoO to Co0)

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Results

TPR XANES

With the uncalcined catalysts, Co(NO3)2 slowly converts to CoOX decomposition products that are

• xidized to a spinel (e.g., Co3O4) –

final light blue spectrum. Afterwards, a typical two step reduction of Co3O4 was observed, with CoO as the intermediate (final dark blue spectrum). Relative to the calcined catalyst, reduction of cobalt oxides occurs

• ver a wider range, indicating

smaller, interacting Co oxide species.

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The temperature range for spectra representing maximum cobalt oxide spinel content was narrow (D = 44 °C) for all uncalcined catalysts, including uncalcined (180 °C), and catalysts containing Pt (197 °C), Ag (206 °C), Re (215 °C), and Ru (171 °C). Results

TPR XANES

Conversion of the cobalt

• xide

spinel to CoO

• ccurred by 315 °C for all

uncalcined catalysts, and the temperature range for spectra representing CoO was narrow (D = 66 °C), with the temperature of maximum CoO content being: uncalcined and catalysts containing Pt, Ag, Re, and Ru. CoO converted to Co0 (final dark blue spectrum to green spectra) with vastly different final extents of reduction by 500 °C depending on the presence

• r absence of promoter, as

well as the promoter identity Pt > Re, Ru > Ag

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Results (1) uncalcined unpromoted catalyst, and uncalcined catalysts promoted with (2) Pt, (3) Ag, (4) Re, and (5) Ru

TPR XANES

Co(NO3)*nH2O in the initial spectra

• f uncalcined

catalysts The point of maximum CoO following reduction of the spinel The point of maximum spinel (e.g., Co3O4) following cobalt nitrate decomposition The point of maximum Co0 content Reference spectra Calcined 12%Co/SiO2

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Results

• Temp. vs Composition

(a) 0.5%Pt-12%Co/SiO2 calcined (c) 0.5%Pt-12%Co/SiO2 uncalcined (e) 0.477%Re-12%Co/SiO2 uncalcined

(b) 12%Co/SiO2 uncalcined (d) 0.276%Ag-12%Co/SiO2 uncalcined (f) 0.259%Ru-12%Co/SiO2 uncalcined

268˚C 297˚C 370˚C 453˚C 520˚C 43% 520˚C 28%

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Results

TPR EXAFS

With the calcined catalyst, Co3O4 is converted to CoO (final dark blue spectrum), with resulting slight shifts in the distances of Co-O and Co-Co coordination. CoO is a short-lived intermediate, and with a slight increase in temperature, a large peak for Co-Co metal coordination is formed (Green).

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Results

TPR EXAFS

With the uncalcined unpromoted catalyst, cobalt nitrate slowly converts to CoOX that oxidizes to a spinel (e.g., Co3O4) (first dark blue spectrum). The spinel converts to CoO (final dark blue spectrum). Once formed, CoO converts very slowly to the metal (green spectra). Even at 500˚C, Co-O coordination is still observed.

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Results

TPR EXAFS

By adding the promoter, the major difference is that significant Co-Co metal coordination peaks begin to form at lower temperature as expected from the TPR and TPR-XANES results, including Pt- promoted 300oC, Re- promoted ~400oC, Ru- promoted ~370oC.

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Results

TPR EXAFS

(1) uncalcined unpromoted catalyst, and uncalcined catalysts promoted with (2) Pt, (3) Ag, (4) Re, and (5) Ru (a) Co(NO3)*nH2O in the initial spectra (b) the point

• f maximum spinel

following cobalt nitrate decomposition, (c) the point of maximum CoO and (d) the point of maximum Co0 content.

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Results

Sample ID

H2 desorbed per gcat [μmol/gcat] Uncorr. Disp. [%] Uncorr. Diam. [nm] % Red. [%] Corr. Disp. [%] Corr. Diam. [nm]

12%Co/SiO2 calcined 10.8 0.98 104.9 49.8 1.98 52.2 0.5%Pt-12%Co/SiO2 calcined 19.3 1.91 54.0 51.4 4.29 24.0 0.5%Pt-12%Co/SiO2 uncalcined 39.2 3.85 26.8 37.0 11.5 8.9 Results of hydrogen chemisorption and pulse re-oxidation.

This table provides an estimate of the average Co metal particle size and extent of reduction obtained from hydrogen chemisorption with pulse reoxidation.

Cobalt particle size differences

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Results

Catalyst CO Conv[%] Selectivity [%] CH4 C2-C4 C5+ CO2 12%Co/SiO2 calcined 13.3 12.5 12.7 73.4 1.4 12%Co/SiO2 uncalcined 40.2 7.3 8.0 84.4 0.3 0.5%Pt-12%Co/SiO2 calcined 30.0 10.1 10.7 78.8 0.4 0.5%Pt-12%Co/SiO2 uncalcined 48.9 8.0 10.2 81.5 0.3 0.276%Ag-12%Co/SiO2 uncalcined 36.8 8.7 14.6 76.4 0.3 0.477%Re-12%Co/SiO2 uncalcined 51.3 6.8 11.7 81.2 0.3 0.259%Ru-12%Co/SiO2 uncalcined 36.8 9.3 9.1 81.2 0.4

CO conversion and product selectivity for the tested catalysts (process conditions: T = 220oC, P= 300 psi, H2/CO= 2 mol/mol, SV = 6 slph per gcat).

LC LCCP Laboratory of Catalysis and Catalytic Processes

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Results

20 40 60 80 100 120 10 20 30 40 50 60

CO conversion (%) T.o.S. (h)

Pt-Co/SiO2 uncalcined Re-Co/SiO2 uncalcined Ru-Co/SiO2 uncalcined Ag-Co/SiO2 uncalcined Co/SiO2 uncalcined Co/SiO2 calcined Pt-Co/SiO2 calcined

Evolution with Time On Stream of carbon monoxide conversion for uncalcined and calcined samples process conditions: T = 220oC, P= 300 psi, H2/CO= 2 mol/mol, SV = 6 slph per gcat.

CO conversion of the unpromoted samples decreased with T.o.S., and the deactivation rate was 0.05%/h for the uncalcined catalyst relative to 0.025%/h for the calcined

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Conclusions  Foregoing calcination and utilizing direct reduction of cobalt nitrate led to the formation of smaller and more strongly interacting cobalt oxide nanoclusters in interaction with silica support as intermediates of the activation process to Co0 nanoparticles; this was demonstrated by TPR, TPR-MS, TPR-XANES, and TPR-EXAFS experiments using hydrogen.  These intermediate cobalt oxides included a spinel (e.g., Co3O4) formed from oxidation of Co2+ species by NO2, which in turn converted to CoO prior to formation of the metal.  To improve the reducibility, metal promoters such as Pt, Re, Ru, and Ag were added.

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 The best catalysts were Re and Pt promoted 12%Co/SiO2 catalysts utilizing direct reduction of the nitrate, where conversions in a CSTR were up to 3.8 times higher and 71% higher than unpromoted and Pt promoted air calcined catalysts, respectively.  At the same time, methane production was lower (6.8 and 8.0% for Re and Pt promoted catalysts by direct reduction versus 12.5 and 10.1% for unpromoted and Pt promoted air calcined catalysts) and C5+ selectivity was higher (81.2 and 81.5% for Re and Pt promoted catalysts by direct reduction versus 73.4 and 78.8% for unpromoted and Pt promoted air calcined catalysts). Conclusions

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Thanks