Eight Catalysts for Change in Human Society

Eight Catalysts for Change in Human Society

Catalysts play a vital role in the advancement of human civilization and global economic development; every major breakthrough in this field has profoundly transformed the way people produce and live. Today, we’ll explore eight catalysts that have changed the world since the Industrial Revolution—each of which gave rise to a new industry.

1. Catalysts for Sulfuric Acid Synthesis

The sulfuric acid industry is one of the most important industries of modern times. In 1875, a German chemist named Jacob established the world’s first production line for fuming sulfuric acid, which used an extremely expensive platinum catalyst—a pioneer in the field of solid industrial catalysts. Ten years later, chemists at the German company BASF developed a more economical and efficient alternative process using V₂O₅ as the catalyst—a material widely used today. It was precisely this sulfuric acid production process that propelled BASF to become the world’s largest sulfuric acid producer at the time.

Types and Functions:

There are numerous types of sulfuric acid synthesis catalysts, each with its specific functions and applications. Common sulfuric acid synthesis catalysts include platinum group metal catalysts, platinum group catalysts, and transition metal catalysts.

1. Platinum Group Metal Catalysts: Metals such as platinum, rhodium, and palladium are important catalysts for sulfuric acid synthesis. They possess high activity and selectivity and can act as oxidizing or reducing agents in the reaction, promoting the sulfuric acid synthesis reaction and thereby increasing the reaction rate and yield.

2. Platinum-group catalysts: These include elements such as platinum, palladium, rhodium, and ruthenium. These catalysts also exhibit excellent catalytic activity and redox properties and play a key role in the sulfuric acid synthesis reaction.

3. Transition Metal Catalysts: These consist primarily of compounds of elements such as molybdenum, tungsten, bismuth, and antimony. These catalysts also possess high catalytic activity and selectivity and are crucial to the sulfuric acid production process.

In addition, there are specific catalysts, such as iron(III) oxide (Market catalyst), titanium dioxide, and silicon dioxide, which also play important roles in the sulfuric acid synthesis process.

In summary, sulfuric acid synthesis catalysts play a crucial role in the production of sulfuric acid. Through the proper selection and use of catalysts, the efficiency and yield of sulfuric acid production can be significantly improved, while also helping to reduce production costs and environmental impact.

2. Ammonia Synthesis Catalysts

If one were to ask what the most important invention in human history is, the ammonia synthesis process developed by German chemist Haber would undoubtedly rank first. The industrialization of the ammonia synthesis process means that humans can use the inorganic gases nitrogen and hydrogen to produce large quantities of ammonia—which is used as nitrogen fertilizer in agriculture—and the industrial-scale supply of nitrogen fertilizer has led to a significant increase in grain production. The emergence of synthetic ammonia spurred the rapid development of the fertilizer industry and other industrial sectors, bringing immeasurable benefits to humanity.

Most importantly, the key factor enabling the successful industrialization of the synthetic ammonia process was the invention of iron-based catalysts. Previously, even under high-temperature and high-pressure conditions, the efficiency of converting nitrogen and hydrogen into ammonia was extremely low. In 1909, German chemist Fritz Haber achieved a 6% yield of ammonia directly by using the metal osmium as a catalyst at 200 atmospheres and 600°C. Two years later, Haber developed a cheaper, more efficient iron catalyst and established an ammonia synthesis plant with a daily production capacity of 30 metric tons. This marked a major triumph for artificial nitrogen fixation, as well as a significant victory for catalysts in the chemical industry and chemical research. For the invention of the ammonia synthesis process, Haber was awarded the Nobel Prize in Chemistry in 1918.

Main Components:

The main components of ammonia synthesis catalysts include transition metal elements such as iron, molybdenum, and nickel, as well as co-catalysts such as aluminum and silicon. These elements play a key role in the catalyst’s activity, stability, and selectivity.

Common Types:

1. Iron Catalysts: One of the most commonly used catalysts in industrial ammonia synthesis. They typically feature iron as the primary active component, combined with other additives and supports to enhance the catalyst’s activity and stability. Under appropriate temperature and pressure conditions, iron catalysts facilitate the combination of nitrogen and hydrogen into ammonia within the reactor. Commonly used iron catalysts include iron-aluminum catalysts and iron-potassium catalysts.

2. Cobalt Catalysts: These are also commonly used in industrial ammonia synthesis. Compared to iron catalysts, cobalt catalysts exhibit higher activity and selectivity, enabling efficient ammonia synthesis at relatively lower temperatures and pressures.

Catalyst Activity:

The activity of ammonia synthesis catalysts is closely related to reaction conditions. For example, iron catalysts exhibit maximum activity at approximately 500°C, which is one of the key reasons why the ammonia synthesis reaction is generally conducted at around 500°C. However, even under optimal conditions, the volume fraction of NH₃ in the equilibrium mixture of the ammonia synthesis reaction is only 26.4%. Therefore, additional measures—such as rapid cooling to convert gaseous ammonia into liquid ammonia and promptly separating it from the equilibrium gas mixture—are necessary to shift the chemical equilibrium toward the formation of NH₃.

3. Fischer-Tropsch Synthesis Catalysts:

In the early 20th century, with the development of the automotive and aviation industries, the demand for liquid fuels increased dramatically, and governments around the world stepped up their investments in finding ways to produce liquid fuels more efficiently and at lower costs. The Fischer-Tropsch synthesis process was invented against this backdrop; it is a process that uses syngas (a mixture of carbon monoxide and hydrogen) as a feedstock to synthesize liquid hydrocarbons under the action of a catalyst and under appropriate conditions. This process was first discovered by German scientists Fischer and Tropsch in 1923; after 13 years of in-depth research, it was finally industrialized in Germany in 1936. Initially, Fischer and Tropsch used a Co-Tu-diatomaceous earth catalyst, but the application gradually evolved to include various supported catalysts such as molten iron, cobalt, and ruthenium, which offered superior catalytic performance.

Main Components and Types:

Fischer-Tropsch synthesis catalysts are primarily composed of transition metals, particularly Group VIII metals in the periodic table, such as Co, Fe, Ni, and Ru. To enhance the catalyst’s activity, stability, and selectivity, auxiliary components—such as metal oxides or salts—are often added. Additionally, catalysts typically require a support material, such as alumina, silica, kaolin, or diatomaceous earth. Among these, iron-based and cobalt-based catalysts are the two most common types used in Fischer-Tropsch synthesis. Iron-based catalysts are classified into low-temperature and high-temperature types, whereas cobalt-based catalysts may not perform as well as iron-based catalysts in certain reactions; therefore, iron-based catalysts are more commonly used in practical applications.

Catalyst Activity and Temperature:

The activity of Fischer-Tropsch synthesis catalysts is closely related to the active components on their surfaces, which typically consist of metal oxides, reduced metals, and iron oxides. Among these, reduced iron is the primary active component in molten iron catalysts for Fischer-Tropsch synthesis; it promotes chemical reactions between gaseous reactants, thereby improving reaction efficiency. The optimal operating temperatures vary depending on the type of metal catalyst. For example, the suitable operating temperature for cobalt and nickel catalysts is 170–190°C, while that for iron catalysts is 200–350°C.

Application Areas:

Fischer-Tropsch synthesis catalysts have widespread applications in the chemical industry. They are not only used in chemical reactions such as ammonia synthesis, methanol synthesis, and synthetic oil production but also play a crucial role in reactions such as the hydrogenation of aromatic hydrocarbons. In addition, these catalysts can be applied in environmental protection fields such as flue gas desulfurization and automotive exhaust purification.

Catalyst Improvement and Optimization:

To enhance the performance of Fischer-Tropsch synthesis catalysts, researchers have conducted extensive improvement efforts. For example, by using different supports and adding various metallic or non-metallic elements as additives, they have modified the catalyst’s properties to achieve higher yields of light olefins. Bimetallic catalysts, such as Fe-Co and Fe-Ru bimetallic catalysts, have also been developed for the Fischer-Tropsch synthesis of low-carbon olefins, offering the advantage of having two metals as active sites.

Production of Fischer-Tropsch Wax:

Fischer-Tropsch wax is derived from crude wax, an intermediate product of the Fischer-Tropsch synthesis, and is an important byproduct of the Fischer-Tropsch process. Prior to the development of the petrochemical industry, the Fischer-Tropsch synthesis process was arguably the most important technology in both the chemical and transportation sectors. Currently, Fischer-Tropsch synthesis is increasingly characterized by higher temperatures, larger-scale operations, and product diversification. Today’s most advanced high-temperature Fischer-Tropsch synthesis units produce not only high-quality petroleum products but also more than 20 to 30 types of high-value-added chemical products, further extending the coal chemical industry chain and expanding the variety of downstream products.

4. Petroleum Refining Catalysts

Almost all petroleum refining processes require catalysts, including catalytic cracking, catalytic reforming, catalytic hydrogenation, alkylation, etherification, and catalytic dehydrogenation and desulfurization. Petroleum refining catalysts account for one-third of the total catalyst market share. The earliest catalysts used were zeolite molecular sieves; X- and Y-type zeolites—particularly Y-type zeolites—remain the primary active components in catalytic cracking processes today. Currently, there is a wide variety of catalysts with diverse properties available for petroleum refining, including ZSM-5, USY, Pt/Al₂O₃, and MoS₂.

Main Types and Applications:

Petroleum refining catalysts primarily include those used in processes such as catalytic cracking, catalytic reforming, hydrofinishing, hydrocracking, isomerization, alkylation, and polymerization. Among these, catalytic cracking, catalytic reforming, and hydrofinishing are the three main types of petroleum refining catalysts. These catalysts help convert crude oil into more valuable chemicals and fuels, such as gasoline, diesel, and lubricating oils.

Catalytic Cracking Catalysts:

Catalytic cracking catalysts are critical to the petroleum refining process. Early on, the primary type of catalyst used was microspherical amorphous aluminosilicate, but this was subsequently and rapidly replaced by rare earth-X, rare earth-Y, and hydrogen-Y zeolite catalysts. In recent years, improvements to these catalysts have included the use of silica or alumina sols as binders to bond zeolites and kaolin, resulting in a new generation of high-density, high-strength semi-synthetic zeolite catalysts.

Catalytic Reforming Catalysts:

Catalytic reforming catalysts are primarily used to improve the octane rating and quality of gasoline. Through the reforming reaction, the catalyst rearranges hydrocarbon molecules in crude oil to produce high-octane gasoline components.

Hydroprocessing Catalysts:

Hydroprocessing catalysts are primarily used to remove impurities such as sulfur and nitrogen from crude oil, thereby improving the quality of petroleum products. During the hydroprocessing reaction, the catalyst reacts with hydrogen to induce hydrogenation of unsaturated hydrocarbons and sulfur- and nitrogen-containing compounds in crude oil, converting them into saturated hydrocarbons and less toxic compounds.

Other Catalysts:

In addition to the three main petroleum refining catalysts mentioned above, there are other catalysts used in specific petroleum refining processes. For example, isomerization catalysts are used to improve the octane number and combustion performance of gasoline, while alkylation catalysts are used to produce high-octane gasoline components.

Improvements and Development of Catalysts:

With continuous advances in science and technology, petroleum refining catalysts are also undergoing constant improvement and development. The emergence of new catalyst materials and preparation methods has significantly enhanced catalyst activity, selectivity, and stability. At the same time, the environmental performance of catalysts has improved, reducing pollutant emissions during the refining process.

Overall, petroleum refining catalysts are a vital component of the petroleum refining process; they play a significant role in enhancing refining efficiency, improving product quality, and reducing environmental pollution. With the continuous advancement of science and technology, more novel and highly efficient petroleum refining catalysts will emerge in the future, providing strong support for the development of the petroleum industry.

5. Chiral-Selective Catalysts

Chiral-selective catalysts are a special class of catalysts characterized by their ability to induce asymmetric reactions, directing reactants to react in a specific direction and thereby achieving chiral selectivity. These catalysts play a key role in the synthesis of chiral compounds and are widely used in fields such as drug synthesis, total synthesis of natural products, polymer synthesis, and chemical sensors. The primary application area for chiral-selective catalysts is in pharmaceutical molecules. Generally, a single molecule contains two isomers that are mirror images of each other; one exhibits pharmacological activity, while the other does not. However, conventional chemical processes typically yield both isomers simultaneously, and the yield of the pharmacologically active isomer may be extremely low. The role of the catalyst is to increase this yield.

The most representative catalytic process is the synthesis of levodopa, used to treat Parkinson’s disease. In 1974, the American company Monsanto developed a highly selective catalyst capable of selectively catalyzing the formation of levodopa during the synthesis reaction, resulting in a product that contained virtually no dopa. This achievement made levodopa the drug of choice for treating Parkinson’s disease. This groundbreaking example can be considered a classic demonstration of the use of catalytic selectivity in chemical production. William Knowles, who was employed by Monsanto at the time and played a pivotal role in this synthetic reaction, was ultimately awarded the 2001 Nobel Prize in Chemistry for this research.

Types of Catalysts

Chiral selective catalysts primarily include chiral metal complexes, chiral organic small molecules, and chiral polymers. These catalysts typically possess specific chiral structures that can form specific spatial configurations with reactants, thereby directing the reaction to proceed in a specific direction. Through the design and synthesis of chiral catalysts, precise control over the reaction process and product structure can be achieved.

Industrial Applications

In drug synthesis, chiral selective catalysts enable the efficient synthesis of chiral drug molecules, enhancing therapeutic efficacy and reducing side effects. In the total synthesis of natural products, chiral catalysts allow for the control of chirality in complex natural products, providing strong support for their development and utilization. Additionally, chiral catalysts can be applied to polymer synthesis to control the stereochemistry and spatial configuration of polymers, thereby enabling the preparation of materials with specific properties.

Synthesis Methods

As research deepens, the design and synthesis methods for chiral selective catalysts continue to evolve. The design and synthesis of novel chiral ligands are central to the field of chiral catalytic synthesis, and their emergence is often closely linked to breakthroughs in this field. Furthermore, by regulating the active sites of catalysts, optimizing reaction conditions, and integrating with other catalytic technologies, the activity and selectivity of chiral selective catalysts can be further enhanced.

Overall, chiral selective catalysts are a class of catalysts characterized by high precision, high efficiency, and high selectivity, offering broad application prospects in the field of chemical synthesis. With continuous advances in science and technology, it is believed that more novel and highly efficient chiral selective catalysts will be developed in the future, making even greater contributions to the development of the chemical industry.

6. Three-Way Catalytic Converter

The primary function of a three-way catalytic converter is to convert toxic compounds in vehicle exhaust—such as CO, NOx, and HC—into CO₂ and water. Because current catalytic converters contain three precious metals—platinum, palladium, and rhodium—they are called three-way catalytic converters. In 1974, the first Clean Air Act was enacted in the United States. At that time, it only regulated CO and HC, and the catalytic converter used for vehicle exhaust treatment was a Pt-Pd oxidation-type catalyst. Later, as photochemical smog caused increasingly severe damage to the air, NOx also became a key indicator for air emissions. In 1989, Ford Motor Company first tested a Pd/Rh catalyst as a component of a three-way catalytic converter, which simultaneously catalyzed the purification of the three harmful pollutants: CO, HC, and NOx. Since then, the three-way catalytic converter has become the standard catalyst in the automotive exhaust treatment industry.

Shape and Structure

The shape of a three-way catalytic converter resembles two decanter bottoms joined together; this design helps increase the contact area between the catalyst and the exhaust gases, thereby improving catalytic efficiency. Its surface is typically marked with relevant parameters for easy identification and use.

Appearance

A new three-way catalytic converter is bright white with a metallic luster. However, as it ages, the catalyst surface may develop discolored spots or slight bluish and purplish streaks, resulting from reactions between the harmful substances in the exhaust gases and the catalyst.

Function

The primary function of a three-way catalytic converter is to oxidize hydrocarbons (HC) and carbon monoxide (CO) in vehicle exhaust into carbon dioxide (CO₂) and water (H₂O), while simultaneously reducing nitrogen oxides (NOx) into nitrogen and oxygen. This process helps significantly reduce environmental pollution caused by vehicle exhaust.

Support and Catalyst

The support component of a three-way catalytic converter is a porous ceramic material. This material possesses excellent heat resistance, corrosion resistance, and mechanical strength, ensuring the stability and activity of the catalyst under high temperatures and harsh conditions. The catalyst consists of metals such as platinum, rhodium, and palladium, which are sprayed onto the support to form catalytic active sites.

Applications

In addition to their use in automotive exhaust treatment systems, three-way catalysts are also widely used in other fields, such as industrial exhaust gas treatment and energy conversion. Through catalytic reactions, three-way catalysts facilitate the conversion of harmful substances, reduce environmental pollution, and improve energy efficiency.

In summary, the three-way catalytic converter is a highly efficient and environmentally friendly catalyst that plays a vital role in automotive exhaust treatment and other applications. With continuous technological advancements and increasingly stringent environmental requirements, the performance and efficiency of three-way catalytic converters will continue to improve.

7. Ziegler-Natta Catalysts

Today, a wide variety of polymer materials—such as synthetic fibers, synthetic resins, and synthetic rubber—have become an indispensable part of people’s daily lives. However, few people realize that the production of all these materials relies on the vast polyolefin industry and the Ziegler-Natta catalysts that have driven the industry’s rapid development. Previously, the polymerization of olefin compounds had to be carried out under high-pressure conditions, and the reaction suffered from numerous shortcomings: excessive side reactions, excessively high pressure, and low polymerization degree.

Originally invented around 1953 by German chemist K. Ziegler (Karl Ziegler) and Italian chemist G. Natta (Giulio Natta), this discovery earned them the 1963 Nobel Prize in Chemistry. Another type of Ziegler-Natta catalyst (Z-N catalyst) was invented in 1955 by Adolf Ziegler and Karl Ziegler using cobalt, aluminum, aluminum chloride, and acid salts. The Ziegler-Natta catalyst is a homogeneous catalyst primarily composed of transition metal salts and alkyl salts of main-group metals. After nearly 70 years of development, the Ziegler-Natta catalyst has evolved from its original homogeneous form to a heterogeneous form.

Main Components and Synthesis:

Ziegler-Natta catalysts primarily consist of titanium tetrachloride (TiCl₄) and triethylaluminum [Al(C₂H₅)₃]. The synthesis process involves the interaction between titanium tetrachloride and organoaluminum compounds. Titanium tetrachloride is first reduced to titanium trichloride, which is then alkylated to yield alkyl titanium chloride. Olefins complex with the vacant sites on the titanium atoms and gradually polymerize into long chains.

Applications and Characteristics:

Ziegler-Natta catalysts are primarily used in the polymerization of olefins, dienes, and other compounds to produce polymers such as polyethylene and polypropylene. They enable olefins to form complexes at the vacant sites on the titanium atoms, thereby gradually polymerizing into long chains. This polymerization reaction exhibits stereoregularity, and the resulting polymers possess high stereoregularity, density, and crystallinity. For example, it has been used in the production of high-density polyethylene, fully stereoregular poly-α-olefins, and highly cis-1,4-poly-diene polymers (such as cis-butadiene rubber and isoprene rubber).

Improvements and Optimization of Catalysts:

With advances in science and technology, Ziegler-Natta catalysts have also undergone continuous optimization and improvement. Not only have complexes been developed through the interaction of alkyl compounds of Group I–III metals with transition metal derivatives of Groups IV–VIII, but ternary and multi-component systems have also been developed, and various types of additives have even been incorporated to enhance catalytic activity and directional effects.

8. Electrocatalysts

Electrocatalysts are substances that accelerate electrochemical reactions and are widely used in energy conversion and storage devices, such as fuel cells, metal-air batteries, and electrochemical cells. They offer numerous advantages, including high reactivity, high selectivity, and high stability, which help lower reaction energy barriers and increase reaction rates, thereby improving the efficiency and performance of these devices. The application of electrocatalysts has primarily emerged alongside the development of the new energy industry.

Over the past decade, as the share of new energy sources has increased and the energy storage market has expanded, the production and use of hydrogen energy have gradually penetrated various industries. In terms of scale, the market share of electrocatalysts remains small; however, countries around the world are currently stepping up their efforts in hydrogen energy. The primary application areas for electrocatalysts are hydrogen electrolysis and fuel cells. In these two fields, precious metal catalysts—such as Pt and Pd—demonstrate superior catalytic activity that no other transition metal catalyst can match. In the fields of fuel cells and hydrogen electrolysis, the greatest technical challenge lies in catalyst synthesis. Currently, countries around the world are increasing their investment in the hydrogen energy industry. It is estimated that by 2050, the global hydrogen energy industry’s output value will reach 20 trillion U.S. dollars.

Classification:

1. The first category consists of catalysts for the production of formic acid or the selective production of formic acid, primarily including Sn, In, Pb, and Hg. These catalysts are characterized by high hydrogen overpotentials and weak adsorption of carbon monoxide. 2. The second category consists of electrocatalysts that selectively produce carbon monoxide, including gold and silver, which feature moderate hydrogen overpotentials and periodic carbon monoxide adsorption capabilities. 3. The third category consists of copper and copper-based catalysts, which feature low hydrogen overpotentials and moderate carbon monoxide adsorption capabilities. These catalysts can be used to synthesize various high-value multi-carbon compounds, such as ethylene, ethanol, propanol, methane, and methanol.

Design and Preparation Methods:

1. Designing electrocatalysts through organic synthesis: Researchers can optimize the electron transfer properties and reaction activity of electrocatalysts by modifying the types and structures of organic groups. 2. Preparing electrocatalysts through the structural design of metal oxide materials: This primarily involves regulating their crystal lattice and cage-like structures to influence electron transfer and mass transfer processes, thereby controlling the catalytic reaction.

Electrochemical deposition is currently one of the primary methods for preparing electrocatalysts. It involves reducing metal ions from an electrolyte onto the electrode surface to form a metal deposit layer, which in turn serves as the electrocatalyst. In addition, methods such as solution heat treatment, hydrothermal synthesis, and flexible template methods are also widely used in the synthesis of electrocatalysts. Overall, electrochemical catalysts play a crucial role in electrochemical reactions; by accelerating reaction rates and improving reaction efficiency, they drive the development of energy conversion and storage devices. In the future, with technological advancements, we can expect to see the development of more efficient and stable electrochemical catalysts, which will make even greater contributions to sustainable human development.