Profile of Researcher

Big Challenge, Big Expectation, an Innovative and An Environmentally-Conscious Research to Adhere Air Pollutant, NOx, to Generate Ammonia

Ph. D/Assistant Professor Masahiro Itoh Course of Materials Chemistry, Division of Applied Chemistry, Graduate School of Engineering, Osaka University

Completed Master's Program for Division of Chemistry, Graduate School of Science, Hokkaido University in March 1998.
Then completed Doctor's Program for Department of Applied Chemistry, Graduate School of Engineering, Osaka University in March 2001.
Became a Ph. D at Osaka University in March 2001.
Became a Research Assistant at Collaborative Research Center for Advanced Science and Technology, Osaka University in April 2001.
Became an Assistant Professor at Center for Advanced Science and Innovation, Osaka University in April 2007.
Became an Assistant Professor at Division of Applied Chemistry, Graduate School of Engineering, Osaka University in April 2011.

The internal combustion engine was invented over 150 years ago. Exhaust from internal combustion engines inevitably contains nitrogen oxide (NOx) . Dr. Masahiro Itoh has focused on the mechanism to form ammonia by chemical reaction between NOx and hydrogen. Forming ammonia by combining a hydrogen permeable membrane and a material to adhere NOx, an air pollutant, would not only eliminate the harmful NOx, but yield a useful chemical. If successful, this technology can yield one quarter of the quantity of ammonia currently produced in Japan. We cannot help but feel excited by this research, although it is only in a first stage of investigation (Phase I)

NOx Is Efficiently Converted To Make Something Useful Out of a Pollutant Through a "Hydrogen Permeable Membrane" Technology

Hydrogen molecules are seldom found in a natural setting, therefore they need to be sourced from fossil fuels or renewable energy sources. When burned, hydrogen generates heat and turns into water, leaving no pollutants behind. There are keen interests by industries, especially the automotive industry, in the use of hydrogen as a clean energy source, due to its high power generation efficiency when used with fuel cells.

"Hydrogen permeable membrane" is a technology utilized to purify hydrogen fuel. Hydrogen permeable membrane generates and purifies hydrogen taking advantage of the property of metals which absorb and store hydrogen to a degree. Once inside a metal, hydrogen becomes atomic and very reactive compared with its molecular state. Hydrogen permeable membrane rapidly permeates hydrogen selectively. Highly reactive atomic hydrogen in the metal may be used as a catalyst. Assistant Professor Masahiro Itoh at Osaka University has been working on converting NOx to ammonia using atomic hydrogen.

Nitrogen oxides are known to be air pollutants. They are what is called NOx, a chemical product of oxygen and nitrogen in the air when something burns. They are generated mainly from factories and automobiles when combusting petroleum and coal. NOx represents nitrogen monoxide (NO) and nitrogen dioxide (NO2) . Researches to efficiently convert both chemicals are much sought after, since NOx gases cause environmental damages such as acid rain and photochemical smog, and are harmful to human health.

Hybridized Catalysts Make It Possible To Combine Nitrogen and Hydrogen Yielding Ammonia

Ammonia (NH3) is generated by chemically combining nitrogen (N2) contained in NOx and hydrogen (H2) . "Haber-Bosch process" is one of the well-known processes for generating ammonia. Nitrogen and hydrogen gases are mixed 1:3 (volume ratio) , pressurized and directly react with each other (N2+3H2→2NH3) at 400 to 500°C while in contact with iron (Fe) catalyst. This is a fundamental process for producing nitrogen-containing chemicals, and is said to be a crucial process in the chemical industry.

In addition to utilizing a hydrogen permeable membrane to form ammonia from nitrogen and hydrogen, Dr. Itoh came up with an idea to hybridize the process using the ruthenium (Ru) -based catalyst in place of an Fe catalyst. He has discovered that ammonia, normally synthesized under medium to high pressure and high temperature (400 to 500°C) , may be synthesized under atmospheric pressure and low temperature range around 100°C, by atomic hydrogen continuously supplied by the hydrogen permeable membrane reacting with nitrogen adhered to the catalyst.

Platinum is used for NOx purification catalyst. "I tried many catalysts. Silver's oxidative capacity is too large, and rhodium's hydrogen reactivity is weak. Platinum has the suitable balance. The amount of platinum used in a catalyst may be reduced by technology using platinum-iron alloy," Dr. Itoh explained.

Ammonia is a very valuable industrial product since fertilizers may be produced from ammonia. In Germany, where Haber-Bosch process was invented, ammonia is used in a large quantity to supply fertilizer containing nitrogen for wheat farming. Ammonia production globally is about 160 million tons, while Japan produces 1.4 million tons domestically. Out of ammonia production, 80% is used to produce fertilizers.

"Approximately 900,000 tons of NOx is generated from recoverable sources. Assuming all NOx is NO2, about 330,000 tons of NH3 may be synthesized. Considering the fact that Japan's domestic demand for ammonia is 1.4 million tons, we will be able to substitute 1/4 of the demand with NH3 generated from NOx. This should trigger a ripple effect throughout the chemical industry," said Dr. Itoh.

Diesel engines are one of the large emission sources of NOx. Since diesel engine's emission gas temperature is low, hydrogen selective catalytic reaction for NOx with low-temperature operation is a promising solution. Dr. Itoh has conducted a study with NOx concentration near 1,000 ppm to simulate diesel exhaust. He took part in a collaborative research on exhaust gas purification technology. He, however, decided to discontinue the research, judging that the system will become too complex for automotive application. He also found out that he needed to improve the hydrogen permeable membrane reactor or a new system where the catalyst actively adheres NOx, since reaction is too slow at low NOx concentration such as 1,000 ppm. He is now looking into applications at large plants, as well as nautical applications for large vessels with diesel engines.

Ph. D/Assistant Professor Masahiro Itoh

This study is characterized by the potential use of relatively reactive NO and NO2 as the nitrogen source in forming ammonia. It makes it possible to convert NOx, a pollutant inevitably generated as long as internal combustion engines are used, to ammonia, a useful chemical industrially, by a reactor combining the hydrogen permeable membrane capable of supplying atomic hydrogen and Pt catalyst with reduced oxygen absorption.

"If my final goal is Phase IV, this study is still at Phase I. At Phase II, I will collaborate with corporations, and refine reactive processes to come up with an efficient prototype reactor. At Phase III, I will increase the capacity of the prototype reactor and continue testing. I would finally like to then create a practical reactor at Phase IV, " said Dr. Itoh. He has a long way toward the practical implementation, since he has just focused on the concept of converting NOx. Uniqueness of this study has motivated the Murata Science Foundation to award a research grant to Dr. Itoh.

Concept of hydrogen permeable membrane reactor

The cathode is made up of Ag-Pd (silver-palladium) hydrogen permeable membrane, and platinum (Pt) coil is placed at the positive pole to generate hydrogen at the negative pole by electrolyzing an aqueous phosphoric acid solution. Generated hydrogen is supplied to the other side of the membrane using hydrogen permeability of Ag-Pd membrane at the negative pole. The reactor controls the amount of hydrogen permeation by adjusting the current. Ammonia is formed by reaction between NOx adhered to the catalyst coated on the external surface of the negative pole and hydrogen.

Concept of hydrogen permeable membrane reactor

Ammonia production process

Currently, synthetic catalysts such as Fe catalyst and Ru catalyst are used to form Ammonia (NH3) . Since the process requires high temperature around 400°C and high pressure over 50 atm, its production energy is large. The process proposed by this study can form ammonia at around 100°C at normal atmospheric pressure, making its production energy very low. This process further converts NOx, a harmful chemical, to a useful chemical.

Ammonia production process