Fast analysis of precious metals Pt, Rh and Pd in car catalytic converters

Introduction

Catalytic converters that are designed to remove toxic gases and pollutants from car exhaust gases contain the precious metals Pt, Pd and Rh. When the car reaches the end of life the converter is scrapped and the precious metals are recovered in a recycling chain comprising several different stakeholders, from scrap yards to toll refineries. Due to their high value, accurate analysis of the precious metal content is critical to ensure every stakeholder receives a fair share for their contribution. This application note shows a safe, easy and accurate method for providing data everyone will trust.

Instrumentation

Measurements were performed using a Malvern Panalytical Epsilon 1 EDXRF spectrometer, equipped with a 50 kV silver (Ag) anode X-ray tube, 6 software-selectable filters, a high resolution SDD10 silicon drift detector and a 1 position sample position.

Sample preparation

Thirty-three car catalyst samples supplied by several customers were used to create the application. The precious metals were determined by fire assay or inductively coupled plasma spectroscopy. The majors in the matrix have been determined using Malvern Panalytical’s solutions WROXI and Omnian. The standards were analyzed in the form of loose powder in a P1 assembled sample cup with a 6 μm polypropylene foil. The setup samples were oven-dried. 8 grams of each powder was put in sample cups and slightly compressed using a steel cylinder, illustrated in Figure 1.

Figure 1. Loose powder sample representation. Loose powders very slightly compressed in the sample cup using a steel cylinder.

Measurement procedure

3 different measurement conditions were used to measure the 3 precious metals and major compounds in the samples. Measuring the total matrix improves the flexibility of the method and makes it applicable for different catalytic converter materials. The total measurement time was set to 5 minutes per sample. In this application note only the three precious metals are reported.

Elements	kV	uA	Filter	Meas. time (s)
Pt , Ni, Zn, Sr, Zr, W, Pb	50	200	Ag	60
Rh, Pd, Ba	50	200	Cu - thick	180
S, K, Ca, Ti, Mn, Fe, La, Ce, Nd	14	714	Al - thin	60

Table 1. Measurements conditions.

Calibration results

Figures 2, 3 and 4 show the resulting calibration graphs for Pt, Rh and Pd in catalytic monoliths. The graphs show very good correlation between the certified concentrations and the measured intensities. Detailed calibration results for the precious metals are listed in Table 2. The RMS (Root Mean Square) value is equivalent to 1 sigma standard deviation.

Compounds	Concentration range	RMS (ppm)*	Correlation Coefficient
Pt (ppm)	0 –1992	52.5	0.9968
Rh (ppm)	0 – 585	10.6	0.9959
Pd (ppm)	0 – 8776	92.6	0.9991

Table 2. Calibration details (* RMS: The more accurate calibrations have the smaller RMS values).

Figure 2. Calibration graph for Pt in catalytic converters

Figure 3. Calibration graph for Rh in catalytic converters

Figure 4. Calibration graph for Pd in catalytic converters

Accuracy and precision

The accuracy and instrument precision were tested by measuring multiple official certified reference materials (CRM’s) 20 times or 5 times consecutively. The certified and average measured concentrations, RMS and relative RMS values are presented in Table 3, demonstrating excellent accuracy and precision.

Sample name (repeats)	Compounds	Certified conc.	Average conc.	RMS	Rel. RMS (%)
NIST 2556 (20x)	Pt (ppm)	697.4 +/- 6.3	695.6	7.2	1.1
	Rh (ppm)	51.2 +/- 0.5	53.9	2.0	3.7
	Pd (ppm)	326 +/- 1.6	322.8	7.2	2.2
NIST 2557 (20x)	Pt (ppm)	1131 +/- 11	1189.6	13.2	1.1
	Rh (ppm)	135.1 +/- 1.9	141.6	2.2	1.6
	Pd (ppm)	233.2 +/- 1.9	236.9	3.6	1.5
ERM-EB504a (5x)	Pt (ppm)	1414 +/- 9.0	1424.8	5.1	0.4
	Rh (ppm)	210 +/- 2.2	216.2	2.3	1.1
	Pd (ppm)	1596 +/- 11	1675.1	18.3	1.1
FLX 133 (5x)	Pt (ppm)	465 +/- 32	462.1	4.0	0.9
	Rh (ppm)	242 +/- 4	237.6	4.0	1.7
	Pd (ppm)	1075 +/- 33	1093.8	15.3	1.4

Table 3. Accuracy and precision testing on four commercially available certified reference materials.

Conclusion

The results clearly demonstrate the capability of Epsilon 1 for the analysis of metals Pt, Rh and Pd in catalytic converters. The repeatable sample positioning, outstanding sensitivity of the optical components combined with powerful software deconvolution algorithms allows the Epsilon 1 to provide accurate analysis for every measurement.

In 5 minutes, the Epsilon 1 will provide an accurate reading of the precious metal content you can trust. The shielding for the high energetic X-rays and safety locks in place guarantees every user safety while determining the value of their sample.