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8 Energetic Reactions with Hydrocarbons
8.2 C–C Bond Cracking—Reactivity of Group V Metal
Oxides
As outlined in the above section how all-metal cluster reactivity with oxygen has been
a continuing topic of interest over the past twenty years; it is of particular interest for
such clusters to enable potential use as energy density materials and energy storage
capability. On the other hand, reactions conducted under endothermic conductions
also have notable implications, such as the ability to acquire large thrust without
undue stress being placed on the aircraft engines and related components, nor the
need to exchange engines on a frequent basis. Moreover, with well selected conditions
the engines operate in conditions of higher efficiency, acquiring better burning rates
and selective reactivity. Among desired conditions, two particularly impact engine
temperatures, namely the use of fuel to act as a coolant and, for the fuel to undergo
desired cracking thereby absorbing energy.
During the last several years Castleman group [2] have been engaged in studying
related problems and during the course of investigations they have identified some
reactions that do display endothermic conditions, finding that in some cases it is
the metal center that plays the dominant role in effecting the reaction class. For
example, Bell et al. [6] showed an investigation into the reactivity and collisioninduced dissociation of vanadium oxide clusters using a triple quadrupole mass
spectrometer coupled with a LaVa-source. As shown in Fig. 8.1a, the dominant peaks
in the mass distribution correspond to (VO 2 ) n (V 2 O 5 ) m (O 2 ) x
+ . Studies on collisioninduced dissociation of V 2 O 4–6
+ , V 3 O 6–9
+ , V 4 O 8–10
+ , V 5 O 11–13
+ , V 6 O 13–15
+ and
V 7 O 16–18
+ indicated that VO 2 , VO 3 and V 2 O 5 units were the core building blocks
for these clusters. Further investigation on the reactivity for these vanadium oxide
clusters towards hydrocarbons showed that the reaction pathways include molecular
association, cracking, dehydration and oxygenation of the neutral hydrocarbons.
For example, the reaction of V 3 O 7
+ with 1-butene (C 4 H 8 ) displays predominant
C−C cracking in forming V 3 O 7 C 2 H 4
+ , while its reaction with 1,3-butadiene (C 4 H 6 )
displays dehydration of the association product, as shown in Fig. 8.1b and c [2].
The variation of C−C cracking and dehydration has been thoroughly investigated
on the VB group metal cluster oxides [3, 6–24]. Figure 8.2 shows the mass distributions of vanadium, niobium, and tantalum oxide cluster cations, and the reactions of
several classes of small organic molecules with cluster oxides composed of vanadium,
niobium and tantalum are displayed in Fig. 8.3 [2]. Note that the n-butene (C 4 H 8 )
displays negligible, small, and predominant C−C cracking for V n O m
+ , Nb n O m
+ , and
Ta n O m
+ , respectively. Similar selectivity was observed for their reactivities with 1,
3-butadiene [2]. It was found that 1, 3-butadine (C 4 H 6 ) displays virtually no C−C
cracking with vanadium oxides, a trivial amount with niobium oxide clusters, while
considerable cracking with Ta oxide clusters.
8 Energetic Reactions with Hydrocarbons
8.2 C–C Bond Cracking—Reactivity of Group V Metal
Oxides
As outlined in the above section how all-metal cluster reactivity with oxygen has been
a continuing topic of interest over the past twenty years; it is of particular interest for
such clusters to enable potential use as energy density materials and energy storage
capability. On the other hand, reactions conducted under endothermic conductions
also have notable implications, such as the ability to acquire large thrust without
undue stress being placed on the aircraft engines and related components, nor the
need to exchange engines on a frequent basis. Moreover, with well selected conditions
the engines operate in conditions of higher efficiency, acquiring better burning rates
and selective reactivity. Among desired conditions, two particularly impact engine
temperatures, namely the use of fuel to act as a coolant and, for the fuel to undergo
desired cracking thereby absorbing energy.
During the last several years Castleman group [2] have been engaged in studying
related problems and during the course of investigations they have identified some
reactions that do display endothermic conditions, finding that in some cases it is
the metal center that plays the dominant role in effecting the reaction class. For
example, Bell et al. [6] showed an investigation into the reactivity and collisioninduced dissociation of vanadium oxide clusters using a triple quadrupole mass
spectrometer coupled with a LaVa-source. As shown in Fig. 8.1a, the dominant peaks
in the mass distribution correspond to (VO 2 ) n (V 2 O 5 ) m (O 2 ) x
+ . Studies on collisioninduced dissociation of V 2 O 4–6
+ , V 3 O 6–9
+ , V 4 O 8–10
+ , V 5 O 11–13
+ , V 6 O 13–15
+ and
V 7 O 16–18
+ indicated that VO 2 , VO 3 and V 2 O 5 units were the core building blocks
for these clusters. Further investigation on the reactivity for these vanadium oxide
clusters towards hydrocarbons showed that the reaction pathways include molecular
association, cracking, dehydration and oxygenation of the neutral hydrocarbons.
For example, the reaction of V 3 O 7
+ with 1-butene (C 4 H 8 ) displays predominant
C−C cracking in forming V 3 O 7 C 2 H 4
+ , while its reaction with 1,3-butadiene (C 4 H 6 )
displays dehydration of the association product, as shown in Fig. 8.1b and c [2].
The variation of C−C cracking and dehydration has been thoroughly investigated
on the VB group metal cluster oxides [3, 6–24]. Figure 8.2 shows the mass distributions of vanadium, niobium, and tantalum oxide cluster cations, and the reactions of
several classes of small organic molecules with cluster oxides composed of vanadium,
niobium and tantalum are displayed in Fig. 8.3 [2]. Note that the n-butene (C 4 H 8 )
displays negligible, small, and predominant C−C cracking for V n O m
+ , Nb n O m
+ , and
Ta n O m
+ , respectively. Similar selectivity was observed for their reactivities with 1,
3-butadiene [2]. It was found that 1, 3-butadine (C 4 H 6 ) displays virtually no C−C
cracking with vanadium oxides, a trivial amount with niobium oxide clusters, while
considerable cracking with Ta oxide clusters.