Measuring the Unmeasurable by IR Spectroscopy: Carbon Deposition Kinetics in Dry Reforming of Methane

Abstract

Dry reforming of methane converts two greenhouse gases to syngas, and Ni catalysts are commonly used for this reaction. A major catalyst deactivation mechanism is carbon deposition. Although numerous kinetic modelling works have been performed on carbon formation, there have been only scarce attempts to measure carbon deposition kinetics under relevant (but not real) conditions, owing to technical difficulties. Here, we report the first successful measurements of the kinetics under real reaction conditions. This was made possible by using a novel algorithm that we have developed. We use IR to measure the molar fractions of unreacted CH and CO , and reaction products, CO and H O, in the effluent from the reactor. By applying the general mass balance principle and the relevant reaction stoichiometries, the carbon deposition rate as well as the flow rates of all these gases in the effluent, including H , are calculated. Compared to the dominant GC-based approach for catalyst performance evaluation, this method has much higher time resolution and much smaller measurement errors.

Controlling the Reduction Extent for Optimal Performance of a Ni/Al2O3 Dry Reforming Catalyst

“…The inconsistence most likely comes from a common practice in catalyst evaluation using gas chromatography (GC), which measures molar fractions of gases in a mixture. As pointed out in the previous work [48], it is a common mistake to calculate the CH 4 and CO 2 conversions using molar fractions measured by GC with the following equation: X i (%) = (1-C i,out /C i,in ) • 100%, where X i (%) is the conversion of a particular reactant, C i,in and C i,out are the influent and effluent molar fractions of the reactant [62,[64][65][66]. In fact, the correct way to calculate the conversion is as equation 4, ,…”

“…4 characteristic peaks at 3135.38 cm -1 , 2391.1 cm -1 , 2021.31 cm -1 , and 1966.24 cm -1 were selected for CH 4 , CO 2 , CO and H 2 O, respectively. Based on the novel algorithm developed previously [48], the molar flow rates of unreacted CH 4 and CO 2 , and reaction products, CO, H 2 O and H 2 , were calculated together with the carbon deposition rate. The conversions of CH 4 and CO 2 were calculated as equations 2 and 3, ,…”

“…Pre-and post-reaction weight measurements give about 85 mg weight gain (see individual measurements in table S2) presumably due to carbon deposition. One advantage of the experimental setup is that it measures all gases involved including H 2 O with high accuracy thus allows carbon deposition rate and H 2 O production rate to be measured [48]. These two rates for all different reduction extents are shown in figure 3.…”