6.2 The B-Spline Model
6.2.3 The B-Spline Model Applied to the Complete Pentanary Sys-
Unfortunately, the extension of the B-Spline algorithm to data sets in more than three dimensions could not be realized so easily. Since this approach could not cope with the predictive power of Kriging the time needed for a complete implementation has been used to improve the Kriging model and to develop several GUIs that allow a convenient access to the implemented Matlab routines.
Experimental Part
This chapter is dedicated to the experimental work that was done to synthesize a complete pentanary composition spread with 1001 samples containing the elements Mn, Co, Cr, Te and Ni. In the following sections, it is explained which metal pre- cursors were employed and used in the acid-catalyzed sol-gel procedure to build the gels on the way to the final catalyst powders. Furthermore, it is explained in detail how the precursor solutions giving the later catalysts were mixed by a dispensing robot, calcined and transferred to the slate library plates to be accessible for the high-throughput screening. An explanation of the high-throughput screening reactor together with the entire setup is given within section 7.3.
7.1 Precursors
All the tested catalysts were prepared by the same synthesis route, following an acid- catalyzed sol-gel process that has been initially explained in section 1.5. Inspired by the work of Schmidt [149] who synthesized a complete pentanary composition spread out of the elements Mn, Co, Mo, Cr and Ni a quite similar approach was realized. Since a large amount of catalyst samples was planned to be synthesized the replace- ment of Mo obtained by the very expensive precursor Molybdenum-isopropoxide was necessary. This was realized by the use of Te instead of Mo after an adequate precursor for Te had been found. For the new compositions the recipe needed to be slightly modified. The incidental subsections deal with the synthesis of the metal propionates as metal ion precursors following the prescriptions described by Saal- frank [141].
7.1.1 Preparation of Cr(III)-Propionate
20,00 g (50.02 mmol) Cr(NO3)3· 9H2O was suspended in 300 ml propionic acid (4.0
mol) in a 500 ml one-necked round-bottomed flask. The reaction mixture was heated
under reflux at 150◦C and constantly stirred. Then, the reflux was removed and the
mixture was boiled at 150◦C for several days while the formation of nitrous oxides
was observed (brown gases, toxic!). If the formation of NOx became less (approx.
after 2-3 days), the excessive propionic acid was removed by a rotary evaporator
operated at 30 mbar and 50 ◦C. As a last step, the product was further dried at
high vacuum (< 1 mbar) at 50 ◦C for several h to end up as a dark green powder
which was further ground in a mortar. To check the composition of the synthesized chromium-propionate, a CHN-analysis was performed. The results are summarized in the following table.
The deviation of the theoretical results from the measured results can be explained by impurities such as amounts of water and traces of nitrate that remained in the powder and could not be removed totally.
C H N
Theoretical Content [%] 39.88 5.58 0
Measured Content [%] 36.98 5.91 0.081
Table 7.1: Results of the CHN-Analysis of Cr(III)-Propionate. 7.1.2 Preparation of Co(II)-Propionate
The synthesis of Co(II)-propionate was realized following the description given by Saalfrank [141] and Spinolo [166].
CoCO3+ 2CH3− CH2− COOH Co(CH3CH2COO)2 + H2O + CO2 ↑ (7.1)
In a 500 ml one-necked round-bottomed flask, 15 g (126.11 mmol) CoCO3 were
suspended in 250 ml propionic acid. The reaction mixture was continuously stirred
and heated under reflux at 150 ◦C for 4 h. After cooling down, the dark violet
suspension was filtered to remove remaining CoCO3. Afterwards, excessive propionic
acid was removed by a rotary evaporator operated at 30 mbar and 50 ◦C. Finally,
the product was further dried in high vacuum (< 1 mbar) at 50 ◦C for several h to
end up as a violet solid. Further grinding in a mortar decreased the grain size. To check the composition of the synthesized chromium-propionate, a CHN-analysis was performed and the corresponding results can be found in the following table:
C H N
Theoretical Content [%] 35.14 4.91 0
Measured Content [%] 36.15 5.21 0.04
Table 7.2: Results of the CHN-Analysis of Co(II)-Propionate.
7.1.3 Preparation of Ni(II)-Propionate
The synthesis of Ni(II)-propionate was realized following the description given by Saalfrank [141].
Ni(OH)2+ 2CH3− CH2− COOH Ni(CH3CH2COO)2+ 2H2O (7.2)
In a 500 ml one-necked round-bottomed flask, 10 g (107.89 mmol) Ni(OH)2 were
and heated under reflux at 150 ◦C for several h (transparent green solution). After cooling down, the excessive propionic acid was removed by a rotary evaporator
operated at 30 mbar and 50 ◦C. Finally, the product was further dried in high
vacuum at 50 ◦C for several h to give a light green solid. Further grinding in a
mortar decreased the grain size. To check the composition of the synthesized nickel- propionate, a CHN-analysis was performed and the corresponding results are given in the following table:
C H N
Theoretical Content [%] 35.18 4.92 0
Measured Content [%] 35.04 5.14 0.078
Table 7.3: Results of the CHN-Analysis of Ni(II)-Propionate.
7.1.4 Preparation of Mn(II)-Propionate
The preparation of Mn(II)-propionate was done using MnO as starting material.
MnO + 2CH3− CH2− COOH Mn(CH3CH2COO)2+ H2O (7.3)
In a 500 ml one-necked round-bottomed flask, 8.33 g (117.46 mmol) MnO were sus- pended in 200 ml propionic acid. The reaction mixture was continuously stirred and
heated under reflux at 150 ◦C for several hours (transparent light brown solution).
After cooling down, the excessive propionic acid was removed using by rotary evap-
orator operated at 30 mbar and 50◦C. Finally, the product was further dried in high
vacuum (< 1 mbar) at 50◦C for several h to give a brownish solid. Further grinding
in a mortar decreased the grain size. To check the composition of the synthesized nickel-propionate, a CHN-analysis was performed and the corresponding results can be found in the following table:
C H N
Theoretical Content [%] 35.84 5.01 0
Measured Content [%] 35.23 4.92 0.075
Table 7.4: Results of the CHN-Analysis of Mn(II)-Propionate.
As the fifth metal precursor, telluric acid (H6TeO6) was used. All solid metal pre-
all catalyst by a sol-gel approach, also propionic acid and a complexing agent (4- hydroxy-4-methyl-2-pentanone) were employed. The propionic acid route described by Saalfrank [141] was applied in a slightly modified way to synthesize all catalysts.