Catalyst Loss on Ignition (LOI) Analysis: Principles, Methods, Standards, and Applications

Catalyst loss on ignition (LOI) analysis is a gravimetric test that quantifies the moisture, volatile matter, and combustible deposits, such as coke, residual organics, and decomposable salts, present in fresh, spent, and regenerated catalysts. By heating a precisely weighed sample to a controlled high temperature and measuring the resulting mass change, accredited third-party laboratories can verify catalyst quality, monitor regeneration efficiency, and establish a consistent dry basis for subsequent elemental analysis. This guide covers the analytical principle, sample types, test items, reference methods, and industrial applications of LOI determination for catalyst materials.

Technical Overview

Loss on ignition (LOI) is defined as the percentage of mass that a catalyst sample loses when it is heated to a specified temperature under controlled atmospheric conditions and held there until the mass change stabilizes. For catalyst materials, the measured loss typically aggregates several contributions: free and physically adsorbed moisture released below approximately 110 °C, structural and crystalline water evolved between roughly 150 °C and 600 °C, combustion of carbonaceous deposits (coke) and organic binders in the range of about 300 °C to 700 °C, and decomposition of carbonates, hydroxides, and residual salts such as nitrates or ammonium compounds at higher temperatures.

An LOI result is always tied to a specific ignition temperature, commonly 550 °C, 600 °C, 750 °C, 950 °C, or 1000 °C, and to the atmosphere used, most often static or flowing air. Because spent catalysts may contain reduced transition metals or metal sulfides that gain mass upon oxidation, for example nickel, iron, vanadium, or sulfided cobalt and molybdenum species, the net LOI can occasionally be zero or even negative. A well-designed LOI protocol therefore states the ignition temperature, atmosphere, hold time, and reporting basis (as-received or pre-dried) explicitly. Although the technique requires only a muffle furnace, a desiccator, and an analytical balance, it underpins critical decisions in catalyst manufacturing, regeneration control, and precious metal recovery.

Testing Samples

Fresh Catalysts and Supports

Typical materials include alumina, silica, silica-alumina, titania, zirconia, and activated carbon supports; zeolites and molecular sieves; and finished shaped bodies such as extrudates, pellets, tablets, spheres, and granules. LOI testing on fresh catalysts verifies residual moisture, confirms the completeness of calcination, and quantifies organic binder content remaining after forming operations.

Spent Catalysts

Spent samples include fluid catalytic cracking (FCC) equilibrium and spent catalysts, hydrotreating and hydrocracking catalysts, reforming, isomerization, and dehydrogenation catalysts, as well as methanol synthesis and ethylene oxide catalysts. For these materials, LOI primarily reflects coke deposition and contaminant species, supporting regeneration decisions and end-of-life evaluation.

Regenerated and Rejuvenated Catalysts

After thermal or chemical regeneration, LOI measurement confirms how effectively carbonaceous deposits have been removed and whether residual volatiles from washing or rejuvenation steps have been eliminated before the catalyst is returned to service.

Catalyst Precursors and Intermediates

Dried filter cakes, hydroxide and nitrate precursors, impregnated but uncalcined supports, and spray-dried powders are tested to track water content and decomposable species through each stage of production, ensuring consistent calcination quality.

Testing Items

Core parameters determined during catalyst LOI analysis include:

• Loss on ignition at a specified temperature (for example LOI at 550 °C, 600 °C, 750 °C, 950 °C, or 1000 °C)
• Free moisture content (mass loss up to 105 to 110 °C)
• Volatile organic matter and residual binder content
• Coke and carbonaceous deposit content (combustible fraction)
• Structural and combined water released from supports and zeolitic frameworks
• Decomposable species such as carbonates, hydroxides, nitrates, and ammonium salts
• Ash or non-volatile residue yield remaining after ignition
• Oxidation mass gain screening for reduced metals and metal sulfides in spent catalysts

Testing Methods

Classical Gravimetric Muffle Furnace Method

The conventional procedure is performed as follows: a clean porcelain, quartz, or platinum crucible is ignited to constant mass and weighed; a homogenized sample, typically 1 g to 5 g for shaped catalysts crushed to a defined particle size, is added and weighed on an analytical balance readable to 0.1 mg; the crucible is placed in a muffle furnace pre-set to the specified temperature and held for a defined period, commonly 1 hour to 4 hours, until constant mass is achieved; the crucible is cooled to room temperature in a desiccator to prevent moisture re-adsorption; and the residue is reweighed. The result is calculated as:

LOI (%) = (m1 − m2) / m1 × 100, where m1 is the mass of the pre-dried (or as-received) sample and m2 is the mass of the ignited residue. Duplicates are run routinely, and repeatability limits are established for each catalyst matrix.

Thermogravimetric Analysis (TGA)

TGA provides a more informative profile by recording mass continuously while temperature ramps at a controlled rate, for example 5 °C/min to 20 °C/min. A typical program heats under nitrogen to approximately 900 °C to strip moisture and pyrolyze volatiles, then switches to air or oxygen to combust the remaining coke. The derivative (DTG) curve separates overlapping events, allowing individual quantification of free water, structural water, volatile organics, and carbon burn-off, in line with the general practice of ASTM E1131 for compositional analysis by thermogravimetry.

Reference Standards and Method Adaptation

While no single universal standard covers all catalyst matrices, LOI procedures are widely adapted from established gravimetric frameworks, including ASTM D7348 for loss on ignition of solid combustion residues, ASTM D3174 and ASTM D3175 for ash and volatile matter determinations, ISO 1171 for ash in solid mineral fuels, and the Chinese national standards GB/T 212 for proximate analysis and GB/T 6284 for loss on drying of chemical products. Method validation, blank crucible corrections, certified reference materials, and defined temperature tolerances are applied by accredited third-party laboratories to ensure traceable and reproducible results.

Applications

• FCC unit monitoring: tracking equilibrium catalyst coke and measuring regeneration efficiency through periodic LOI screening
• Hydrotreating and hydroprocessing: assessing carbon laydown and metals contamination to decide between regeneration, rejuvenation, and replacement
• Manufacturing quality control: verifying moisture, binder burnout, and calcination completeness of supports and finished catalysts against specifications
• Analytical basis correction: converting ICP-OES, XRF, and other elemental assay results to a dry, LOI-free basis for consistent metal loading certification
• Research and development: evaluating thermal stability, hydrothermal dealumination behavior, and washcoat or binder formulation studies
• Precious metal recovery and trading: establishing volatile and combustible content for the valuation and processing of spent PGM-bearing catalysts
• Environmental compliance: characterizing spent catalyst waste streams for classification, disposal, or recycling pathways

FAQ

What ignition temperature should be selected for catalyst LOI?

The temperature depends on the analytical objective. Temperatures around 550 °C to 600 °C are suitable when the focus is coke and organic burn-off while preserving carbonate and structural components; 950 °C to 1000 °C is used when total volatile and decomposable species, including carbonate carbon dioxide and zeolitic structural water, must be captured. The selected condition should always accompany the reported value.

Why can LOI be negative for some spent catalysts?

When a spent catalyst contains reduced metals, sulfides, or lower oxides, exposure to air at high temperature converts them to higher oxides, increasing the residue mass. If this oxidation mass gain exceeds the mass lost by volatiles and coke combustion, the calculated LOI becomes negative, which is a well-documented phenomenon for sulfided hydrotreating catalysts and metal-contaminated FCC catalysts.

How does LOI differ from ash content?

LOI measures what is driven off or burned away during ignition, while ash content measures the incombustible inorganic residue that remains. The two are complementary, and together they provide a full mass balance of the volatile and non-volatile fractions of a catalyst sample.

Should the test be run in air or an inert atmosphere?

Air or oxygen is used when the goal is total combustible content, since coke requires oxygen to burn. A nitrogen pre-step, most conveniently performed by TGA, separates moisture and pyrolysis volatiles from the combustion event, giving a cleaner coke quantification and reducing the risk of sample ignition excursions.

What sample size and preparation are required?

A representative sample of approximately 1 g to 5 g is typical, with shaped catalysts gently crushed and homogenized to ensure uniform heating, while avoiding over-grinding that could alter moisture content. Pre-drying at 105 °C to 110 °C may be specified when LOI is to be reported on a dry basis.