The article contains sections titled: 1. Introduction 2. Properties 2.1. Physical Properties 2.1.1. Single‐Component Systems 2.1.2. Two‐ and Multicomponent Systems 2.2. Chemical Properties 2.2.1. Chemistry of Helium, Neon, and Argon 2.2.2. Chemistry of Krypton 2.2.3. Chemistry of Xenon 2.2.4. Radon Compounds 2.2.5. Molecular Structures of Noble Gas Compounds 2.2.6. Noble Gas Clathrate Compounds 3. Occurrence and Availability 3.1. Terrestrial Occurrence 3.2. Occurrence of Radioactive Isotopes 3.3. Lunar and Solar Occurrence 4. Extraction and Isolation 4.1. Isolation From Air 4.1.1. Helium and Neon 4.1.2. Argon 4.1.3. Krypton and Xenon 4.2. Helium Extraction from Natural Gases 4.2.1. Crude Helium Extraction 4.2.1.1. Low‐Temperature Fractionation 4.2.1.2. Crude Helium Extraction by Permeation Processes 4.2.2. Purification of Helium 4.2.2.1. Purification of Helium by Pressure Swing Adsorption 4.2.2.2. Other Processes for Purification of Helium 4.2.3. Example of a Complete Process 4.3. Isolation of Argon from Ammonia Purge Gases 5. Liquefaction of Helium 5.1. Processes for Liquefaction of Helium 5.1.1. Recuperative Processes 5.1.2. Regenerative Processes 5.2. Gas Purification for Helium Liquefiers 5.3. Examples of Helium Cryo Plants 5.3.1. Liquefier Using the Claude Process 5.3.2. Liquefier Using the Stirling Process 5.3.3. Helium Cryo Plant Using the Gifford ‐ McMahon (GM) Process 5.4. Process Developments 6. Quality Specifications and Analysis 7. Uses 7.1. Welding 7.2. Illumination 7.3. Other uses 8. Storage and Transportation 9. Economic Aspects

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The article contains sections titled: 1. Conventional Uses 1.1. Hydrogen in the Chemical Industry 1.1.1. Ammonia Synthesis 1.1.2. Hydrogen in Refinery Processes 1.1.3. Hydrogen in Coal Refinement 1.1.4. Synthesis Gas 1.1.5. Hydrogen in Organic Synthesis 1.1.6. Hydrogen in Inorganic Synthesis 1.2. Hydrogen in Metallurgy 1.3. Other Uses 2. Hydrogen Energy 2.1. Aims of the Hydrogen Energy Economy 2.2. Production Systems for Hydrogen Energy 2.2.1. Energy Sources 2.2.2. Production Methods for the Energy Carrier Hydrogen 2.3. Hydrogen‐Energy Conversion Systems 2.3.1. New Developments for Hydrogen Storage 2.3.1.1. Cryoadsorption 2.3.1.2. Hydride Technology 2.3.1.3. Liquid Organic Hydrogen Carriers 2.3.2. Combustion and Heating 2.3.3. Hydrogen Fuel Systems 2.3.3.1. Hydrogen Propulsion Systems for Space 2.3.3.2. Hydrogen as Aviation Fuel 2.3.3.3. Hydrogen for Automotive Vehicle Transport 2.3.4. Electricity Generation from Hydrogen 2.3.4.1. Heat ‐ Power Processes 2.3.4.2. Electrochemical Energy Conversion 2.4. Future Developments 2.4.1. Production Schemes 2.4.2. Hydrogen Energy Economics 2.4.3. International Research

The article contains sections titled: 1. Production from Coal and Hydrocarbons 1.1. Coke Oven Gas 1.2. Gasification of Coal and Hydrocarbons 1.2.1. Coal Gasification 1.2.2. Gasification of Liquid and Gaseous Hydrocarbons 1.2.3. Examples of Industrial Scale Hydrogen Production (by Partial Oxidation of Hydrocarbons) 1.3. Catalytic Reforming of Hydrocarbons 1.3.1. Feedstocks 1.3.2. Tubular Reformer 1.3.3. Steam Reforming Plant 1.3.4. Special Designs 1.3.5. Autothermal Reactors 1.4. Refinery Processes 1.5. Petrochemical Processes 2. Electrolysis 2.1. Principles 2.2. Conventional Water Electrolysis 2.3. New Developments in Electrolytic Processes 2.4. Hydrogen as Byproduct from other Electrochemical Processes 3. Thermochemical Water Cleavage 3.1. Thermodynamics of Closed Cycles 3.2. Further Criteria of Thermochemical Cycles 3.3. Thermochemical Cyclic Processes 3.4. Hybrid Cycle Processes 4. Other Methods for the Cleavage of Water 4.1. Thermolytic and Radiolytic Processes 4.2. Photochemical or Photoelectrical Water Cleavage 4.3. Hydrogen Formation in Biological Systems 5. Other Chemical Processes 5.1. Hydrogen from Conversion of Metals 5.2. Hydrogen from Ammonia 5.3. Hydrogen from Methanol 5.4. Hydrogen from Hydrogen Sulfide 5.5. Hydrogen as Byproduct 6. Economic Aspects 6.1. Analysis of the Cost Structure 6.2. Prognosis of the Hydrogen Costs

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