Nanocatalytic Spontaneous Ignition and Self-Supporting Room-Temperature Combustion

Abstract

Stable and reproducible spontaneous self-ignition and self-supporting combustion have been achieved at room temperature by exposing nanometer-sized catalytic particles to methanol/air or ethanol/air gas mixtures. Without any external ignition, structurally supported platinum nanoparticles instantaneously react with the gas mixtures. The reaction releases heat and produces CO 2 and water. Such reactions starting at ambient temperature have reached both high (>600°C) and low (a few tenths of a degree above room temperature) reaction temperatures. The reaction is controlled by varying the fuel/air mixture. Catalytic activity could be dramatically changed by reducing particle size and changing particle morphology.Catalysis is a well-known process in which a catalyst aids in the attainment of chemical equilibrium by reducing the free energy of transition-complex formation in a reaction pathway. Catalytic reactions have very wide and vitally important applications in the chemical, petroleum, energy, and automobile industries as well as in many other fields. 1 Normally, however, heterogeneous catalysts are not sufficiently active at room temperature and require external heat for ignition (generally, reaction temperatures are >200°C); the preheating requirement for a catalytic reaction can be very costly for industrial applications. 2 The search for catalysts that are sufficiently active at room temperature and that are also able to rapidly convert large amount of reactants has a long history. 3 Here we report a method to achieve spontaneous self-ignition and selfsupporting combustion of alcohols at room temperature by using nanometer-sized catalytic particles and no source of external ignition.Energy stored in the form of chemical bonds (i.e., gasoline or methanol) is most often converted to thermal energy first rather than directly to other forms of energy such as mechanical or electrical energy. Conventionally, such energy conversion occurs at high temperature, and external ignition generally is required to initiate the combustion or burning process. Modern internal combustion engines (ICEs) were designed on the basis of the Carnot cycle and built by taking advantage of such energy conversion processes in which sophisticated and complex ignition systems govern the performance and quality of the engine. Such ignition processes require an external energy source (such as a battery) and other supporting systems (such as a controller) that greatly increase the complexity of each system and potentially reduce the energy utilization efficiency. On average, the efficiency of an ICE is ∼21%; in contrast, an advanced fuel cell converts chemical energy directly to electrical energy and can yield higher energy conversion efficiency (∼51%). 4 Nevertheless, temperatures of a few hundred degrees are typically required to carry out such reactions, while heat-related energy losses represent ∼20% of total energy produced. However, high reaction temperatures may not be an absolutely necessary step in energy conversion processes. New de...

Catalysis of Methanol‐Air Mixture Using Platinum Nanoparticles for Microscale Combustion

“…The catalyst substrates involved in the standard cycling tests were observed to be reusable as long as the period between two experimental runs did not exceed 48 hours. It is assumed that the catalyst material experiences poisoning or degradation when exposed to ambient air for prolonged period of time, as suggested by other researchers [24,27,32]. Extensive work has been performed in the field of nanoparticle catalysis on preventing degradation of these nanometer sized particles when exposed to relatively high temperatures.…”

“…Platinum nanoparticles have been previously demonstrated to self-ignite small alcohols, notably methanol-air, at room temperature and their reactivity is particle size dependent [24]. Nominal particle sizes, as large as 500 nm, have been tested with methanol-air premixtures and nearly complete oxidation was achieved without the need to preheat the catalyst [24,25].…”

“…Nominal particle sizes, as large as 500 nm, have been tested with methanol-air premixtures and nearly complete oxidation was achieved without the need to preheat the catalyst [24,25]. Additionally, size-dependent catalyst activity was also established, with increased activity observed for smaller nanoparticles [2,25].…”

Size dependence of nanostructures: Impact of bond order deficiency

“…This is because Pt-or Pd-based catalysts currently used in automobile exhaust cleanup are inactive below a temperature of 200 C. Interestingly, low-temperature gold catalysts are very inactive unless the gold is in the form of particles smaller than w8 nm in diameter [418]. However, self-ignition and selfsupporting combustion of Pt nanoparticles have been observed [419] at room temperature by exposing the particles to methanol/air or ethanol/air gas mixtures. The reaction is controlled by varying the fuel/air mixture and reducing particle size.…”

Nanopowder molding method for creating implantable high-aspect-ratio electrodes on thin flexible substrates

“…The deionized water vaporizes during the high-temperature sintering and does not leave any impurities within the conductive structure. Methanol, ethanol, and other alcohols are not suitable surfactants for mixing a Pt slurry because the Pt nanoparticles can ignite methanol and ethanol vapor at room temperature [14].…”