1. Batches of 1 kg of VAlO(3) & BiMo(4)
Understanding the role of shaping in the preparation of heterogeneous catalysts: graphite as tableting agent
Víctor G. Baldovino-Medranoa,*, Minh Thang Leb, E. Bruneelc, Isabel Van Driesschec, B. Farina, Eric M. Gaigneauxa,*
aUniversité catholique de Louvain, Institute of Condensed Matter and Nanosciences - IMCN, Division « MOlecules, Solids and reactiviTy – MOST », Croix du Sud 2, box L , B-1348 Louvain-la-Neuve, Belgium
bDepartment of Petrochemistry, Hanoi University of Technology, Dai Co Viet Street 1, Hanoi, Vietnam
cDepartment of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, 9000 Ghent, Belgium /
Objective
Conclusions
Graphite as tableting agent of VAlO and BiMo:
Acts as a lubricant for the process:
It forms a layer between the tablets and the die of the tableting machine which is necessary for continuous production.
Is an effective binding agent:
It increases the mechanical resistance to compression of the tablets
Affects surface area (SABET) as follows:
Positive for non-porous BiMo (increase in SABET)
Negative for mesoporous VAlO (decrease in SABET)
Modifies the catalytic performance:
It favored ODHP for calcined VAlO  Good guy
It disfavored catalytic performance for non-calcined VAlO and BiMo  Necessary evil
To analyze the role of graphite as a shaping agent for vanadium-aluminium mixed (hydr)oxides (VAlO) and bismuth molybdates (BiMo)
 VAlO and BiMo are Selective oxidation catalysts.
Catalyst shaping is
Context
Necessary in industry
Seldom studied in catalysis science(1)
Commonly done by Tableting
Graphite as additive
is a “necessary evil”(2)
poorly understood
Experimental
Catalyst preparation
Catalytic tests
Characterization
Analysis of reaction products:
On-line GC
TCD and FID detectors to quantify the reaction products: O2, C3H8, C3H6, C3H4O and COx.
Expression of the results
Intrinsic conversion and yield
Xj = molar conversion
Yj = molar yield
j = C3H8 or C3H6
w = catalyst mass (g)
SABET = BET surface area (m2×g-1)
Performed in every stage of the process:
Before and after tableting
For fresh and spent catalysts
500 mm > Dp ≥ 350 mm, VAlO-xG-NC/C
400 mm > Dp ≥ 250 mm, BiMo-xG-NC
Grinding & Sieving +
Batches of 1 kg of VAlO(3) & BiMo(4)
Sieved to particles size ≤ 100 mm
Graphite (G)
x = 0, 1, 3, 7 wt.% 4h
VAlO-xG-NC
VAlO-xG-C
Method:
co-precipitation
VAlO (hydroxide)
BiMo (oxides)
Mechanical strength for tablets
Axial tensile strength (σZ)
Instron 5566 machine
Physisorption (N2 & Kr) at 77K
Surface Area (SBET) & Porosity
Micromeritics Tristar and ASAP 2010
Textural properties
SEM Microscopy
JSM-35 C, JEOL
Chemical state
XPS
SSI-X-probe spectrometer
Crystallinity
XRD
D8 Brüker Advanced diffractometer
Molecular structure
Raman
InVia apparatus from Renishaw
Oxidative dehydrogenation of propane
(ODHP) for VAlO-xG-NC/C
Nomenclature
VAlO-xG-NC
BiMo-xG-NC
NC = non calcined
Gas Flow: 40 mL/min
C3H8/O2/N2= 10/15/75 (vol %)
T = 748 K
Propylene oxidation to acrolein
for BiMo-xG-NC
Mixing
“Rolling bottle”
Tableting
Hand operated machine
Tablets
L = 2.3 mm
ϕ = 5.1 mm
Gas Flow: 59 mL/min
C3H6/O2/N2= 2.5/2.5/95 (vol %)
T = 698 K
Patm
Fixed-bed continuous reactor
Results & Discussion
Effect of graphite on the tableting process
Effect on the mechanical resistance and SABET
Chemical state of the catalysts
A continuous process for tableting of VAlO and BiMo was not possible without graphite
+ Graphite
VAlO-xG-NC
Graphite was a lubricant that formed a shiny layer on the rim of the tablets
BiMo-xG-NC
Upon calcination:
VAlO-xG-C tablets cracked due to water release not to graphite burning
Graphite was evenly distributed within the catalyst particles
SEM image of BiMo-xG-NC particles
1 wt.% Graphite was enough to boost the mechanical resistance of the catalysts
SABET increased for BiMo  non-porous material
SABET decreased for VAlO  mesoporous material
 Changes in surface area can be associated to pore widening during tableting
Surface area of VAlO-xG-NC and BiMo-xG-NC catalysts
Mechanical resistance of VAlO-xG-NC and BiMo-xG-NC
BiMo-xG-NC
XPS C 1s spectra for VAlO-xG-NC/C (fresh & spent)
BiMo-xG-NC
Except for the presence of the graphite, C-C component, no apparent changes in the chemical state of the catalysts (VAlO-xG-NC/C & BiMo-xG-NC) was observed
Graphite effect on the catalysts structure
Effect on the catalytic performance
XRD analysis of BiMo-xG-NC (fresh & spent)
Raman spectra of VAlO-xG-NC/C
Catalytic performance of VAlO-xG-NC/C in ODPH
Graphite band
The structure of VAlO-NC/C was modified by calcination but not by the presence of graphite
For calcined VAlO-xG-C graphite was a promoter
No variation in the XRD pattern of BiMo
No variation in the XRD pattern of BiMo-xG-NC
Catalytic performance of VAlO-xG-NC in ODHP
Catalytic performance of VAlO-xG-C in ODHP
Conclusion
Graphite did not induce molecular level effects on the structure of the catalysts
Graphite had a negative effect on non-calcined catalysts; VAlO-xG-NC and BiMo-xG-NC
Acknowledgements
Authors acknowledge the financial support of Fonds Speciaux de Recherche (UCL), the Marie Curie Actions of the EU-FP7 and the “DGTRE, Région Wallonne”, project “DEPOLAIR” Convention No M.T. Le thanks the Vietnam National foundation for Science and Technology (NAFOSTED) for funding (Project No )
Calcination of VAlO-xG-NC could have caused the formation of oxygen functional groups favorable to ODHP
References
Catalytic performance of BiMo-xG-NC in propylene oxidation to acrolein
(1) S. Mitchell, N.-L. Michels, J. Pérez-Ramírez, Chem. Soc. Rev. 42, 6094 (2013)
(2) A.B. Stiles, T.A. Koch, in Chemical Industries, Catalyst Manufacture 2nd ed., Marcel Dekker (1995) pp
(3) V.G. Baldovino-Medrano, B. Farin, E.M. Gaigneaux, ACS Catalysis 2, 322 (2012)
(4) V.G. Baldovino-Medrano, M.T. Le, I. Van Driessche, E. Bruneel, E.M. Gaigneaux, Ind. Eng. Chem. Res. 50, 5467 (2011)