Crude oil drawn from the ground yields straight-run gasoline through atmospheric and vacuum distillation, with an octane number of typically only forty to sixty — put that straight into a modern engine and it will knock violently.

Raising the octane number into the nineties depends mainly on one unit: catalytic reforming. And at its core is a bed of platinum supported on alumina.

This is one of platinum's earliest large-scale commercial applications. UOP's Platforming process went on stream in 1949 and has not been replaced in the seventy-plus years since.

1. What Reforming Actually Changes

"Reforming" changes molecular structure, not carbon number. The feedstock is a naphtha fraction (roughly C6–C11), which passes through the platinum catalyst bed under a hydrogen atmosphere at about 500 °C and a set pressure, undergoing four classes of reaction:

Dehydrogenation of naphthenes to aromatics. Cyclohexanes lose six hydrogens to become benzene rings. This is the principal octane-boosting reaction; it is fast and strongly endothermic, and thermodynamically favoured at high temperature.

Dehydrocyclization of paraffins. Straight-chain alkanes first cyclize, then dehydrogenate to aromatics. This is the hardest step and the key reaction determining how severe the unit must be run.

Isomerization. Straight chains become branched chains, and the octane number rises sharply. Iso-octane is defined as octane number 100 and n-heptane as 0 — that difference is exactly what this reaction exploits.

Hydrocracking. Large molecules crack into smaller ones. This is an unwanted side reaction — it consumes hydrogen, produces light gas components, and reduces liquid yield.

Reforming output has two value streams: high-octane reformate (fed straight into the gasoline blending pool), and by-product aromatics (benzene, toluene and xylenes — BTX — the foundational feedstocks of the chemical industry). It also produces large quantities of high-purity hydrogen; reformers remain to this day the principal hydrogen source for many refineries, supplying hydroprocessing and hydrocracking units.

2. Bifunctional Catalysis: Platinum and Alumina Each Do Half the Work

This is the most elegant design in catalytic reforming. The catalyst is not a single-function material but two functions working together:

Metal function (platinum): handles dehydrogenation and hydrogenation. Naphthene dehydrogenation, and the dehydrogenation steps within paraffin dehydrocyclization, all occur on platinum sites.

Acid function (chlorided alumina): handles isomerization and cyclization. The alumina support is treated with chlorinating agents (1,2-dichloroethane, tetrachloroethylene and the like) to create Lewis and Brønsted acid centres.

The two are joined by a spillover mechanism: the alkane is first dehydrogenated to an olefin on platinum, the olefin migrates to an acid centre for isomerization or cyclization, then returns to platinum for hydrogenation or further dehydrogenation.

The engineering implication is very concrete: the system must maintain both metal activity and acid strength simultaneously, and an imbalance in either degrades performance. Loss of chloride means insufficient acidity and poorer isomerization; excess chloride means acidity that is too strong, intensified hydrocracking and lower liquid yield. Industrial units therefore inject chloride and water continuously, holding the water/chloride ratio within a very narrow window — this is the core technical skill of reformer operation.

3. Semiregenerative and Continuous: Two Process Routes

The principal cause of reforming catalyst deactivation is coking, and the process divides into two types accordingly:

Semiregenerative reforming. After a run of some months to a year or two, the whole bed is taken offline and coke is burned off in situ. Equipment is simple and investment low, but activity declines toward the end of the run, requiring a rise in reaction temperature to compensate, with the product slate shifting along with it.

Continuous catalyst regeneration (CCR). Catalyst circulates continuously between the reactors and the regenerator; coked catalyst is constantly withdrawn, burned and returned. This sustains a constant high activity and permits operation under more severe conditions, with both aromatics yield and hydrogen production higher. Modern large units take this route as the mainstream; representative processes are UOP's Platforming (CCR type) and Axens' Octanizing.

CCR places far higher demands on catalyst mechanical strength — the catalyst circulates repeatedly through the system and endures attrition, and fines formation directly causes plugging and loss. At selection, this is a specification of equal weight to activity.

4. How the Metal Formulation Has Evolved

Early practice used monometallic platinum. Bimetallic and multi-metal systems followed:

Platinum–rhenium (Pt-Re): rhenium improves stability and coke tolerance, permitting lower-pressure operation and higher octane. Common in semiregenerative units.

Platinum–iridium (Pt-Ir): high activity but somewhat poorer selectivity; used mainly in continuous reforming.

Platinum–tin (Pt-Sn): suppresses hydrogenolysis and reduces coking; one of the mainstream formulations for continuous reforming.

Formulation choice is tied directly to unit type, target product (gasoline-mode or aromatics-mode) and operating pressure. "More advanced" is not automatically better.

5. Poisoning: Feedstock Pretreatment Decides Success or Failure

Reforming catalysts are extremely sensitive to impurities, so the feed must pass through hydrotreating before entering the reformer:

Sulfur: interacts strongly with platinum and is the main source of reversible poisoning. Hydrotreating converts organic sulfur to hydrogen sulfide for removal, and the sulfur content entering the unit must be reduced to a very low level.

Nitrogen: basic nitrogen compounds neutralize the acid centres on the support, knocking out the acid function directly. Its damage is often more insidious than sulfur's — sulfur poisoning shows up as declining dehydrogenation activity, whereas nitrogen poisoning shows up as poorer isomerization and an octane number that will not come up.

Arsenic: alloys with platinum, causing permanent, irreversible poisoning. This is the most dangerous class; refineries processing high-arsenic crudes must install dedicated arsenic removal facilities.

Lead, copper, sodium and other metals: likewise irreversible poisons, originating mainly from upstream contamination and equipment corrosion.

Field experience says this: most performance problems in a reforming unit trace back to the feedstock, not to the catalyst itself. The diagnostic sequence should be — first check the desulfurization, denitrogenation and dearsenication performance of the pretreatment units, then check the water/chloride balance, and only last suspect the catalyst.

6. Recovery: Spent Catalyst Is a Platinum-Bearing Asset

Although the platinum content of reforming catalyst is only a few tenths of one percent, the charge is measured in tonnes, so the precious-metal value of a single unit is considerable. At turnaround, spent catalyst goes through a pyrometallurgical or hydrometallurgical flowsheet to recover the platinum (and the precious-metal fraction of any rhenium, iridium or tin present), at high recovery rates along a mature path.

At procurement and settlement, the assay protocol for platinum content, sampling representativeness, and the deduction rules for moisture and residual oil must all be agreed in writing up front — disputes in this area are not uncommon in the industry.

7. Its Place in the Energy Transition

Some ask: with electric vehicles spreading and gasoline demand falling, does reforming still have a future?

Three points are worth noting. First, the aromatics produced as a by-product are foundational chemical feedstocks, and their demand does not move in step with gasoline. Second, the by-product hydrogen holds stable value as refinery hydroprocessing intensity continues to rise. Third, platinum catalysts' capability in high-temperature hydrocarbon conversion extends to reforming of biomass and renewable feedstocks.

So precious-metal demand from this production line will not decline in step with gasoline consumption; the change will be structural rather than in total volume.

8. The One-Sentence Summary

Catalytic reforming is the veteran of platinum's industrial applications, and the most successful industrial example of bifunctional catalysis: platinum handles dehydrogenation, alumina handles isomerization and cyclization, and spillover joins the two — turning low-value straight-run naphtha into high-octane gasoline, aromatics and hydrogen.

The core of its operation is not how advanced the catalyst is, but the fine control of three things: impurity levels in feedstock pretreatment, the water/chloride balance, and the rhythm of coking and regeneration.



Diethylenetetramethyldisiloxane platinum complex (platinum catalyst) MY 8116