ساخت و ارزیابی کاتالیزور‌های مخلوط اکسیدی Mn- Fe- Ce در واکنش احتراق فقیر متان (LMC)

نویسنده

دانشکده مهندسی شیمی، دانشگاه تفرش، تفرش، ایران

چکیده
موضوع تحقیق: در پی احتراق ناقص متان در خودروهای گازی، توربینها و ... آلاینده‌های زیست‌محیطی از جمله متان نسوخته منتشر می‌شود. بدین ترتیب به‌کارگیری فرایندهایی که احتراق کامل متان را در دماهای پایین میسر می‌سازند لازم است. احتراق کاتالیزوری فقیر متان، فرایندی موثر برای استفاده از این منبع فسیلی (سنتزی) و مهار آلاینده‌های مربوطه است. با وجود تحقیقات گسترده، تهیه کاتالیزور‌هایی با فعالیت و پایداری حرارتی بالا و دمای شروع واکنش پایین، همچنان از مسائل چالش‌ برانگیز در این زمینه محسوب می‌شود.

روش تحقیق: در این تحقیق کاتالیزور‌های مخلوط اکسیدی منگنز- آهن و منگنز-آهن ارتقا داده‌ شده با سریم در واکنش احتراق فقیر متان با نسبت اکسیژن به متان برابر 6 به 1، در محدوده دمایی oC 200 تا oC 550 مورد بررسی قرار گرفتند. کاتالیزور مخلوط اکسیدی منگنز-آهن به روش هم‌رسوبی به همراه ماده‌ی فعال سطحی CTAB و کاتالیزور مخلوط اکسیدی منگنز-آهن ارتقا داده ‌شده با سریم به روش تلقیح مرطوب تهیه شدند.

نتایج اصلی: کاتالیزور منگنز-آهن فعالیت بالایی در واکنش احتراق فقیر متان از خود نشان داد. دمای تبدیل %10، 50% و %90 متان در این کاتالیزور به‌ ترتیب oC 305، oC333 و oC437 به‌ دست آمد. فعالیت بالای این کاتالیزور را می‌توان به سطح ویژه بالا (m2.g-1 9/59)، حالت‌های مختلف اکسیدی این ساختار (خواص اکسایش-کاهش) و قابلیت ذخیره‌سازی اکسیژن به ‌وسیله اکسید منگنز ارتباط داد. درکاتالیزور منگنز-آهن ارتقا داده‌ شده (%5 وزنی سریم) فعالیت کاتالیزوری بهتری نسبت به کاتالیزور منگنز-آهن در دماهای بالا حاصل شد. درکاتالیزور ارتقا داده ‌شده میزان تبدیل 90% در دمای oC 421 حاصل شد، هرچند تغییر محسوسی در دمای تبدیل %50 و %10 متان مشاهده نشد. افزودن سریم به مخلوط اکسیدی منجر به پایداری بهتر کاتالیزور در دمای oC 500، پس از 5 ساعت شد. کاتالیزور ارتقا داده ‌شده با سریم پس از 5 ساعت در جریان واکنش، هیچ‌گونه افتی نشان نداد؛ درحالی‌که برای کاتالیزور مخلوط اکسیدی منگنز-آهن کمتر از %2 افت مشاهده شد.

کلیدواژه‌ها

موضوعات


عنوان مقاله English

Synthesis and evaluation of Mn-Fe-Ce mixed oxide catalysts in lean methane combustion reactionon reaction

نویسنده English

atieh ranjbar fordoei
Department of Chemical Engineering, Tafresh University, Tafresh 39518 79611, Iran
چکیده English

Research subject: Research subject: Incomplete combustion of methane in natural gas vehicles, gas turbines, and other sources releases environmental pollutants, including unburned methane. Thus, employment of processes that provide complete combustion of methane at low temperatures is necessary. Lean catalytic methane combustion is an efficient process for controlling environmental pollutants while utilizing methane as a fossil (or synthetic) fuel source. Despite extensive research, the development of catalysts with high activity, thermal stability, and low light-off temperature remains a significant challenge in this field.



Research approach: In this study, manganese-iron mixed oxide catalysts and Ce-promoted manganese-iron mixed oxide catalysts were evaluated for lean methane combustion under the following conditions: an oxygen-to-methane ratio of 6:1 and temperatures ranging from 200°C to 550°C in 50°C increments. The manganese-iron mixed oxide catalyst was synthesized using a surfactant-assisted co-precipitation technique, while the Ce-promoted manganese-iron mixed oxide catalyst was prepared via a wet impregnation method.

Main results: The Mn-Fe catalyst showed great catalytic activity in lean methane combustion. The temperatures corresponding to 10%, 50%, and 90% methane conversion (light-off temperatures) for the Mn-Fe catalyst were 305°C, 333°C, and 437°C, respectively. The high catalytic activity of the Mn-Fe catalyst was attributed to its high BET surface area (59.9 m2·g-1), the redox properties of the mixed oxide, and the oxygen storage capacity of manganese oxide. The Ce-promoted Mn-Fe catalysts exhibited relatively higher catalytic activity compared to the unpromoted catalyst in lean methane combustion. 90% methane conversion was achieved at 421°C (T90) for the promoted catalyst, while no significant changes were observed in the temperatures corresponding to 10% and 50% methane conversion. The addition of Ce as a promoter enhanced the catalyst's stability at 500°C after 5 hours on stream. The promoted catalyst exhibited no decrease in catalytic activity, whereas the unpromoted catalyst showed a decrease of less than 2% in catalytic activity.


کلیدواژه‌ها English

Methane Combustion
Manganese
Iron
Cerium
Catalyst
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