ruthenium starting material.
Outlined in this chapter are attempts to produce gels of RUO2 and a mixed RUO2- Ti0 2 system via the alkoxide route along with partial charge calculations on a number of ruthenium alkoxide species. We began with attempts to prepare mixed Ru0 2-Ti0 2
systems since TiOg gels are known to be straightforward to prepare and indeed RUO2- Ti0 2 gels had been reported earlier by Kameyama et al®.
4.2 Instrumentation
Many of the instrumental techniques are described in chapter 2. In addition thermal analysis was performed using a TA instruments SDT 2960 simultaneous is thermogravimetric analysis (TGA) and is differential thermal analysis (DTA) machine.
Powder X-ray Diffraction (XRD) analysis was performed using a Siemens D-
500 diffractometer using the powder method with Cu IQ (Ni filtered) source. The scan range used was 20_=_1O-9O'^ with a step size of 0.02° . The scan rate was 0.5° 20 per minute continuous scan. The patterns were compared to RUO2 and Ti0 2 data (JCPDS
21 -1172 and JCPDS 21-21-1272, respectively). Some analysis was performed on a
STOE STADI X-Ray diffractometer.
For XPS (X-ray photoelection spectroscopy) analysis the six samples were mounted on specimen stubs using double sided adhesive tape and analysed using
MgKa radiation at 170 W using 7.5 mm slits and 80/40 eV pass energies.
Transmission electron microscopy (TEM) analysis was performed using a
Philips EM400T electron microscope (100 kV, a C2 aperture of 50 pm and a
diffraction aperture of 30 pm). For scanning electron microscopy (SEM) analysis the
were placed on clean aluminium stubs. When dry these were coated with gold .
Typical features were analysed by energy dispersive analysis of X-rays (EDX).
4.3 Results and Discussion
We begin with an account of our attempts to prepare mixed Ru0 2-Ti0 2 gels by
sol-gel processing. We start with an account of the synthetic procedure followed
4.3.1 Attempted Sol-Gel Studies on RuOz-TiOz Mixed Oxides
In non-aqueous sol-gel processing we require alcohol soluble precursors, preferably alkoxides. Following the method of Kameyama® we attempted to generate ruthenium alkoxides in situ from RuCl3.nH2 0 and sodium alkoxide (1:3) ratio (equation 4.1)
RuCla + 3NaOR -> Ru(OR)3 + 3NaCl (4.1)
Thus six Ru0 2-Ti0 2 mixed oxides were prepared by generating solutions of
ruthenium alkoxides from commercial RUCI3and sodium ethoxide solution (Table 4.1)
under reflux in anhydrous alcohol. After cooling the solution was mixed with Ti(0 Et)4 and then hydrolysed using water with acid, base or no catalyst. Hydrogen peroxide, H2O2, was then added to all samples to oxidize Ru (III) to Ru (IV). The gels or
powders obtained were dried under vacuum to remove residual solvent. The ruthenium to titanium ratio was kept at 4:1 at all times to investigate the effects of different catalysts on the final product.
Chapter 4: Non-Aqueous processing o f RUO2
Hydrolysis of the precursors using NH3 (sample 1) and water (samples 2 and 3)
gave powders in agreement with the previous work of Kameyama et aŸ. Hydrolysis of
the ruthenium alkoxides using HNO3 as a catalyst gave a mixture of gel and powder
almost instantaneously which dispersed and then re-gelled upon addition of hydrogen
peroxide. Hydrolysis using HNO3 in a large volume gave a black sol and ultimately gave brown powders after several days. This is in contrast to the other experiments which gave black products. Hydrolysis of the isopropoxide precursor gave a gel within
10 minutes of the commencement of hydrolysis. Upon addition of peroxide, however,
black particles were obtained.
Sample^ ruthenium alkoxide [Ru]*’ hydrolysis catalyst
1 ethoxide 0.16M NH3(EtOH)
2 ethoxide 0.16M none
3 ethoxide 0.32M none
4 ethoxide 0.16M HN03(aq)
5 ethoxide 0.04M HN03(aq)
6 isopropoxide 0.16M HN03(aq)
a) Typically water, catalyst and hydrogen peroxide (100 volumes) are added to 4mmol Ru and 1 mmol Ti (after 12mmol NaOR added to generate ruthenium ethoxide) in alcohol to give final ratio = 5:1:0.1. b) Initial concentration of ruthenium before addition of NaOR,
Table 4.1 : Ruthenium precursors and catalysts used in production of Ru0 2-Ti0 2 mixed
It is not in any way surprising that hydrolysis using base or neutral conditions gives powders, as according to Livage et al*, these conditions will not lead to gels
unless the alkoxide precursor is chemically modified due to fast condensation. Use of acid catalysts with eüioxide precursors would appear to give a gel as long as the conditions are not too dilute. In the case of the high dilution experiment it would appear that the concentration of the precursors (« 0.05M) is too low for them to be able to form a continuous network and that the powders obtained are a mixture of partially condensed hydr oxide species. The brown colour of the final product does suggest that it is not the same as that produced by hydrolysis and condensation using base or neutral conditions which give black powders. The addition of peroxide, which can speed up the rates of both hydrolysis and condensation, may then increase the rates of both reactions to the extent that the formation of particles is favoured over gelation. It is also possible from the long time taken to produce any precipitation that the solution may be too dilute. A further consideration must be the catalytic decomposition of H2O2 by RUO2.2H2O. If the RUO2 is hydrated then this decomposition will raise the hydrolysis ratio (the ratio of water to metal) of the mixture and also the temperature of the solution and thus the nature of the final product will be affected.
In the case of the isopropoxide precursor the fast gel time relative to the ethoxide precursor suggests two possible explanations, i) The ruthenium ethoxide precursor
may be oligomeric, like Ti(0 Et)4, and the isopropoxide is monomeric. The oxidation
state of metal alkoxides are generally less than their normal coordination numbers leading to oligomerization or, in the case of bulky groups, such as isopropoxide, for which oligomerization cannot occur, solvent coordination, ii) Alternatively, after Ti(0 Et)4 addition to Ru(0 ‘Pr)3 mixed precursors are produced containing OEt and 0 ‘Pr
groups which hydrolyse and condense at different rates. Supercritical drying of the 114