(213b) Superior Composite Oxide Catalysts for Combustion of Volatile Organic Compounds

Introduction

Volatile organic compounds (VOC), along with sulfur oxides, nitrogen oxides and ammonia, are among the major contributors to environmental pollution. The primary sources of VOC are emissions from industrial processes and transportation exhaust. In the manufacture of most consumer products, some processing steps involve the use of organic compounds. These VOC may be solvents for pigments, silicones, coating materials, or unreacted feedstock or decomposition products, such as hexane, toluene, alcohols and alkanes.

Catalytic combustion is an efficient approach for VOC abatement at mild temperatures (300-500°C). Typical commercial VOC combustion catalysts are Al₂O₃-supported Pt and Pd, coated on monoliths. Due to the high cost of the precious metals and poor tolerance to Si and P poisons, alternative low-cost transition metal oxide catalysts have been actively investigated in recent years, including perovskites and mixed transition metal oxides. In this abstract, NexTech Materials will report excellent VOC combustion performance on composite oxide catalysts at low temperatures.

 Materials and Methods

The composite oxide catalysts were prepared using a deposition-precipitation approach.  The catalyst testing was run in a fixed bed reactor under the conditions of 200-400⁰C, 0.05-0.5% VOC and balance air.  The gas compositions were analyzed by GC and MS.

 Results and Discussion

The testing data indicated that composite oxide catalysts could oxidize VOC (e.g., ethane, propane, butane, hexane, butene, toluene and propanol) to CO₂ and H₂O at 200-500⁰C and gas hourly space velocities of 45,000-150,000 ml/g-hr. The temperature for complete conversion of VOC on the composite oxides was 150⁰C lower than that on conventional precious metal catalysts under the same reaction conditions. The oxide catalysts were also more tolerant to silicon and phosphorous, two common impurities in VOC stream, than the precious metal catalysts.  100% conversion was achieved at 200⁰C for n-propanol and 300⁰C for hexane on SiO₂ and P₂O₅ poisoned composite oxide catalyst. Preliminary lifetime testing results indicated that the catalyst was stable in VOC combustion reactions. Deactivation was not seen during ~900 hrs on stream.

The composite oxide catalysts were conducted to ethanol combustion testing for bakery exhaust treatment as well as hydrocarbon and CO combustion testing for lean-burn natural gas combustion engine. Sulfur tolerance has been improved on some oxide catalysts, which is critical for natural gas engine applications. The above results have demonstrated that the low-cost transition metal oxides are good catalyst candidates for VOC removal.

The catalysts were characterized with BET, TPR, XRD and TEM. TEM analysis showed that nano-size particles (5-10 nm) and sub-micron size (0.05-0.2 micron) were formed on the catalysts. The nano-sized particles contributed to the high combustion activity.