As the primary source of activity for catalytic oxidation reactions, vanadium is typically dispersed on the support surface in the form of polyvanadates in practical catalysts.
A key innovation in vanadium-titanium catalyst design, featuring:
Strong Interaction: The special strong interaction between V₂O₅ and anatase TiO₂ enables high dispersion of vanadium species, forming a monolayer or sub-monolayer coverage. This significantly enhances vanadium utilization efficiency and prevents sintering-induced deactivation.
Toxicity Resistance: TiO₂ supports exhibit excellent tolerance to SO₂ in reaction gases, avoiding deactivation caused by sulfation (a common issue with traditional Al₂O₃ supports).
Stability: The anatase phase maintains structural stability under catalytic reaction temperatures.
WO₃ or MoO₃: Primarily stabilize the anatase phase, inhibiting its transformation into the catalytically inactive rutile phase to improve thermal stability. They also regulate surface acidity and electronic properties.
SiO₂, Al₂O₃, etc.: Usually used as binders or structural aids to enhance mechanical strength.
High Activity and Selectivity: The high dispersion of vanadium species fully exerts their redox capabilities, delivering exceptional activity and selectivity for target oxidation reactions (e.g., SO₂ oxidation, NH₃-selective catalytic reduction of NOₓ).
Excellent Sulfur Poisoning Resistance: A key reason for replacing traditional vanadium-aluminum or platinum-based catalysts. The weak interaction between TiO₂ surfaces and SO₂ prevents the formation of stable sulfates.
Good Thermal Stability: Maintains structural stability within a wide temperature window (typically 300-450°C) in the presence of promoters.
High Mechanical Strength: Suitable for industrial fixed-bed or honeycomb reactors.
Vanadium-titanium catalysts serve as the "heart" of two major industrial processes:
Function: Efficiently catalyze the oxidation of SO₂ (generated from pyrite or sulfur combustion) to SO₃, which is then used to produce sulfuric acid. This is the standard catalyst adopted by 100% of modern sulfuric acid plants.
Reaction: 2SO₂ + O₂ ⇌ 2SO₃
Function: Used for waste gas treatment in stationary sources (e.g., coal-fired power plants, steel mills) and mobile sources (e.g., marine engines). In the presence of oxygen, ammonia (NH₃) acts as a reducing agent to selectively convert toxic nitrogen oxides (NOₓ) into harmless nitrogen (N₂) and water (H₂O).
Reaction: 4NO + 4NH₃ + O₂ → 4N₂ + 6H₂O (main reaction)
Technical Status: SCR technology is currently the most widely used and mature flue gas denitrification technology globally, with vanadium-titanium catalysts as the mainstream option. Catalyst formulations (V₂O₅-WO₃/TiO₂ or V₂O₅-MoO₃/TiO₂) are optimized based on flue gas conditions (temperature, composition).
Selective oxidation of organic compounds (e.g., partial processes for o-xylene oxidation to phthalic anhydride).
Simultaneous flue gas desulfurization and denitrification (DeSOₓ/DeNOₓ) technology.
Vanadium-titanium catalysts are manufactured in various shapes to adapt to different industrial equipment:
Pellet/Ring Shape: Mainly used in fixed-bed reactors for traditional sulfuric acid production.
Honeycomb Shape: The primary form for SCR denitrification systems, offering high porosity, low pressure drop, large specific surface area, and anti-clogging properties.
Plate Shape: Suitable for high-dust flue gas environments, featuring extremely high mechanical strength.
Vanadium-titanium catalysts are highly mature industrial products, with complete systems established for their preparation, application, and recycling.
Low-Temperature Activity: Developing low-temperature (< 200°C) SCR catalysts to adapt to lower flue gas temperatures or eliminate flue gas reheating is a key focus (e.g., manganese-based, cerium-based catalysts).
Poisoning Resistance: Further improving tolerance to poisons such as As, alkali metals (K, Na), and heavy metals.
Vanadium-Free Formulations: Due to vanadium's biological toxicity and price volatility, developing high-performance non-vanadium-based SCR catalysts (e.g., Fe-based, Cu-based, Ce-based) is a long-term research hotspot.
Spent Catalyst Recycling: Efficiently recovering valuable metals (V, W, Ti) to achieve resource circulation and environmental protection.
Vanadium-titanium catalysts are critical pillar materials for modern industry, particularly in environmental protection and basic chemical sectors. With V₂O₅-WO₃(MoO₃)/TiO₂ as the core formulation, they dominate the multi-billion-dollar markets of sulfuric acid production and flue gas denitrification, thanks to their high activity, selectivity, exceptional sulfur resistance, and stability. It is no exaggeration to state that modern clean energy utilization and chemical production would not be feasible without efficient vanadium-titanium catalysts. Future development will focus on performance optimization, low-temperature adaptability, and environmental friendliness.
