The protolytic cracking of n-pentane and n-heptane were conducted in a tubular flow reactor with a quartz tube with an internal diameter of 7 mm at ambient pressure. Catalyst pellet (300 - 500 µm) were activated in situ at 813 K with a heating ramp of 10 K min^-1 for 1 h in 20 ml min^-1 synthetic air and then flushed for 30 min with 20 ml min^-1 N2. The reactant stream was introduced into the reactor via an evaporator, using N2 as a carrier gas. The reaction was carried out between 733 and 793 K. The molar ratio between N2 and n-heptane was kept at 100. Reactant and products were separated and analysed by on-line chromatography (Superlco Q-Plot, capillary column: 30 m × 0.53 mm × 2.0 µm) using an FID detector.

n-heptane (Wako, > 99 %) was used as the reactant. The catalytic cracking of n-heptane was carried out in a continuous flow fixed bed reactor. Nitrogen was used as a carried gas. Each reaction condition was listed in the supplementary part. A syringe pump was used for the feeding of n-heptane. Both of USY (IRZ-FAU001) and ZSM-5 (IRZ-MFI001) were pressed, crushed and sieved to 150-250 μm granules and then a 15-100 mg catalyst was loaded and sandwiched by two layer of silica wool in the reactor (The diameter of glass pipe was 4 mm). Depended on the type of catalysts, the heights of catalyst bed of 50 mg USY and ZSM-5 were 9mm and 7mm, respectively. Before reaction, the catalyst was pretreated in a 50 ml/min nitrogen stream at 813 K for 1 h and then was cooled down to the reaction temperature 773 K. In the activity test, n-heptane conversion at 5 min after introduction the reactant to the catalyst bed was measured as initial conversion and reaction was carried for 90 min. The mole ratio between nitrogen and n-heptane was kept at 100.
The unreacted n-heptane at reactor outlet was analyzed using gas chromatograph (GC-2025, Shimadzu) equipped with an FID detector using a capillary column (DB-35), one of the products methane was analyzed using a GC-14B equipped with FID detector (Gaskuropack 54) and other gaseous products (C2, C3 C4) were analyzed by GC-14 equipped with TCD detector (Unipak S).
The conversion, selectivity and carbon balance were calculated by flowing substrate (Flow_i) and defined by following equations:
Conversion = Σα_i×Flow_product-i / (Σα_i×Flow_product-i+7×Flow_{n-heptane-out});
Selectivity_product-i = α_i×Flow_product-i/Σα_i×Flow_product-i;
Carbon balance = (α_i×Flow_product-i+7×Flow_{n-heptane-out})/(7×Flow_n-heptane-in);
Reaction rate was based on formation rate of products:
Rate = Σ×Flow_product-i