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Hierarchically porous Pd/C catalysts in
nitrobenzene flow hydrogenations
Brennen Lummus
1
Importance of Hydrogenation
• Hydrogenation of vegetable oils to make margarine and shortenings [2]
• Hydrocracking in the petrochemical industry [1]
• Production of specialty chemicals such as aniline and cyclohexane [4,6]
• Commercially performed using heterogeneous catalysts – supported Ni, Pd, or Pt [5]
2
Hierarchically Porous Catalysts• Hierarchy of pore sizes in the
structure
1.Less potential for coking of catalyst
2. Increased accessible surface area and metal dispersion [3]
3.Decreased metal particle size
• Theoretically: Longer lifetime, greater product conversion
3
Advantages
Reactor Design
5
Reactor Assembly
Packed-bed Down-flow Constructed with glass and polyethylene tubing
6
Flow and Temperature Controls
• Gas Flow: rotameter, range of 0-65 cm3/min
• Liquid Flow: syringe pump with 60 mL plastic syringe
• Temperature: temperature control unit with K-type thermocouple and heating tape
7
Catalyst Loading
• Pre-heat, catalyst bed, and post-bed zones
• ½ inch ID glass tube
• Catalyst and 1 mm glass beads
8
Model Reaction-Hydrogenation of Nitrobenzene
• 3:1 Hydrogen to Nitrobenzene stoichiometric ratio
• Problem: Hydrogen is a gas, reactor volume is small
• Low Flow – prevent pressure build-up
Parameters studied
• Amount of catalyst• Temperature• Residence Time• Metal Loading• Type (manufacturer)
N
O
OH
3 H2
NH2
H2O2
9
Qualitative Observations
• Catalyst eventually deactivates
• Product concentrations change
• Accompanied by color changes
10
Terms to Know• Activity: How fast the reaction proceeds in the presence of the
catalyst
• Conversion: Moles reactant converted Moles of reactant fed
• Selectivity: Moles product X formed Moles reactant converted
• Reactivity: General term for the overall “strength” of the catalyst
• Residence Time: How long the substrate spends in the reactor bed
11
Major Possible Products
NH2
HN
HN
NH2
Aniline Cyclohexylamine
N-cyclohexylaniline Diphenylamine
12
Results - Catalyst Mass
• Conditions: 230 °C, .07 mL/min NB, 60 cm3/min H2, 1% Pd/C ThruPore catalyst
• Very similar results
NH2
HN
HN
NH2
HN
HN
13
Results- Temperature
• Conditions: .07 mL/min NB, 60 cm3/min H2, 1% Pd/C ThruPore catalyst
• Higher Temp: greater initial by-product concentration, deactivation occurs sooner
NH2
HN
HN
NH2
HN
HN
14
Results - Residence Time
• Conditions: 230 °C, .07 mL/min NB, 60 cm3/min H2, 1% Pd/C ThruPore catalyst
• Conditions: 230 °C, .03 mL/min NB, 30 cm3/min H2, 1% Pd/C
ThruPore catalyst
• Delayed Deactivation
NH2
HN
HN
NH2
HN
HN
15
Results- Metal Loading• Conditions: 230 °C, .07 mL/min NB,
60 cm3/min H2, 2.0 grams ThruPore Catalyst
• Deactivation seen sooner in 0.5% and 2% metal loading catalysts
16
NH2
HN
HN
Results- Commercial Comparison
• Conditions: 230 °C, .07 mL/min NB, 60 cm3/min H2, 2.0 grams 1% Pd/C catalyst
• Neither deactivates, commercial – higher aniline selectivity
17
Conclusions• Commercial catalyst is more selective
for the hydrogenation of nitrobenzene to aniline
• ThruPore catalyst is more reactive
• Catalyzes a deamination reaction alongside hydrogenation
• Yields by-products, N-cyclohexylaniline and Diphenylamine, in significant proportions
N
O
O
NH2 NH2
HN
+H2
+3 H2
-NH3
Hydrogenations
Deamination
18
Future Prospects• Study more substrates – styrene,
benzene, dichlorobenzene, maleic acid
• Determine mechanism of the deamination reaction
• Continuous improvement of reactor – glass syringe, MFC, flow meter with broader range
Cl
Cl
HO OH
OO
19
References
1) "The Hydrocracking Process." Refining NZ. Refining NZ, n.d. Web. 28 July 2016.2) "Hydrogenation of Unsaturated Fats and Trans Fat." Chemwiki. N.p., 01 Oct. 2013. Web. 28 July
2016.3) Kotbagi, T. V., et al. (2015). "Novel one-pot synthesis of hierarchically porous Pd/C monoliths by a
co-gelation method." MRS Communications 5(01): 51-56.4) Li, C. H., et al. (2005). "Nitrobenzene hydrogenation with carbon nanotube-supported platinum
catalyst under mild conditions." Journal of Molecular Catalysis A: Chemical 226(1): 101-105.5) Sangeetha, P., et al. (2009). "Hydrogenation of nitrobenzene over palladium-supported catalysts
—Effect of support." Applied Catalysis A: General 353(2): 160-165.6) Solymosi, F. (1968). "Importance of the Electric Properties of Supports in the Carrier Effect."
Catalysis Reviews 1(1): 233-255.
20
Acknowledgements• ThruPore and NSF for the funding to carry out this project
• Dr. Vincent and the University of Alabama REU program for this opportunity
• Dr. Martin Bakker and Dr. Trupti Kotbagi for advice and guidance
• Dr. Qiaoli Liang for training and assistance on the GCMS software
21
Heterogeneous Catalysts
• Phase of catalysts differs from the phase of the reactants
Homogeneous
Heterogeneous
Conversion and Selectivity Clarification
Example:
• Run 100 g of NB through reactor• Product consists of 50 g NB, 40 g
aniline, and 10 g diphenylamine
• Conversion is 50%• Selectivity is 80% aniline, 20%
diphenylamine
22
Chromatogram and SpectrumTP DC 2.118 LF RUN 1, HR 17, '4'
Time1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00
%
0
100BAKKER-072016-4 Sm (Mn, 2x1) Magnet EI+
TIC1.34e6
Area, HeightArea%70.6117.6511.74
Area142139.1935522.3623636.50
Height1252044452655299336
Time4.31
10.2210.70
4.311421391252044
10.2235522
452655 10.7023636299336
TP DC 2.118 LF RUN 1, HR 17, '4'
m/z62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100
%
0
100
BAKKER-072016-4 187 (4.285) Cn (Cen,2, 80.00, Ht); Cm (186:187) Magnet EI+ 6.55e493.166.0
65.0
64.063.0
92.1
67.178.077.076.075.0
91.190.0
94.1
95.1
(m a in lib ) A n iline60 64 68 72 76 80 84 88 92 96 100 104 108
0
50
100
63
65
66
6774 76 78 86 88 91
92
93
9495
NH2
23
Why Vapor Phase?
• Greater kinetics
• Solubility of hydrogen is low in nonpolar liquids
• Less transverse force on catalyst particles by gas compared to liquid
24
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