The Impact of Platinum, Palladium and Rhodium in Spent Automotive Catalytic Converters

Important factors in the recycling, trading and purchasing of spent catalytic converters are the highly variable compositions and volatile prices of platinum group metals (PGMs), such as rhodium (Rh), palladium (Pd) and platinum (Pt), especially now.

The demand in 2020 for Ph, Pd and Pt totaled 21.2, 308, and 215 tons, respectively. The automotive catalyst industry1 consumed about 90% of the total Rh1, 85% of the total Pd and 32% of the total Pt.

The physical recycling begins with decanning, or the removal of the shell and extraction of the honeycomb-shaped material inside the catalytic converter.

The physical recycling begins with decanning, or the removal of the shell and extraction of the honeycomb-shaped material inside the catalytic converter. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

In the same year, 7.3 tons of Rh, 41.2 tons of Pd and 33.7 tons of Pt were recovered through the use of recycling activities, mainly from spent catalytic converters; at the 2020 cumulative average price of fine metals, this represents a total value of about $12 Billion.

Figure 1 shows how the prices of Rh, Pd and Pt have fluctuated strongly over the last 15 years depending on speculation, demand and supply.

Pt, Pd, and Rh prices 2006-20212.

Figure 1. Pt, Pd, and Rh prices 2006-20212. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

The fluctuations coupled with tightening emission regulations have directly impacted the compositions of the catalysts, which has in turn strongly influenced demand. The prices of Rh and Pd spiked in 2020-2021 because of a deficit in the supply.

In terms of PGM composition, the value of a single catalytical converter can vary anywhere from less than $100 to more than $1000. These materials are often ground into a powder and blended when traded, meaning that it is of the utmost importance for recyclers and traders to be able to:

  • Catch material that has been fraudulently adulterated and blended
  • Get or pay a fair price
  • Identify blends or single catalytical converters with high PGM levels 

The ability to accurately and in real-time determine the contents of Rh, Pd and Pt in spent automotive catalytical converters is invaluable in order to avoid considerable financial losses and maximize profit. 

Thermo ScientificTM NitonTM Handheld XRF Analyzers

Thermo Scientific offers an entire range of handheld XRF analyzers for accurately quantifying Rh, Pd and Pt in automotive catalytical converters: 

  • The best accuracy and precision is offered by the XL3t 951 and 981 GOLDD+, which are the high models and are equipped with a high performance, large-area silicon drift detector and a 50 kV tube
  • The mid-range models are the Norton SL3t 501 and 8-1 analyzers, which provide more accurate and precise results for PGMs with their filter changer that allows for optimum beam conditions and 50 kV
  • Great value for money is provided by the Niton XL2 501 analyzer, which maintains a high level of performance for PGMs 

Both the XL3t 951 and 981 GOLDD+ also detect light elements, including Phosphorus, silicon, aluminum and magnesium and are more sensitive to detect low levels of PGMs. They also have a shorter measurement time to enhance productivity.

The Automotive Catalyst Mode is pre-calibrated and uses a fundamental parameter approach (FP), an algorithm that uses theoretical constants for the influence of all elements contained in the sample to correct. 

FP can be used for analyzing the spent materials, which often show unprecedented composition variability. 

A key consideration for obtaining accurate results for Rh, Pd and Pt is the measurement of rare earth elements, as well as lead, zirconium and other elements potentially present at high levels in spent catalysts.

Sample Preparation

The collected ceramic substrate catalysts undergo a de-canning operation in which the ceramic is extracted using a honeycomb structure from the steel case. Either metallic substrate or ceramic substrate is used to make automotive catalyst material. 

Usually, the ceramic substrate is cordierite coated using a PGM-containing wash coat. This means that the entire ceramic goes through the process of being sorted, crushed, milled and often blended with other catalysts.

Source: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

Model XL2 501 XL3t 501/801 XL3t 951/981 GOLDD+
 
Tube max voltage1 45 kV 50 kV 50 kV
Detector technology2 Si-PIN Si-PIN SDD
Optimum number of beams for PGMs / total number of beams3 1 for PGMs/1 2 for PGMs/3 2 for PGMs/4
Typical total measurement time 80 seconds 120 seconds 60 seconds
Limits of detection (3 σ)4 Pt: 20 ppm

Pd: 13 ppm
Rh: 13 ppm
Pt: 16 ppm
Pd: 7 ppm
Rh: 6 ppm
Pt: 10 ppm
Pd: 5 ppm
Rh: 5 ppm
Accuracy5 ** *** ***
Precision6 * ** ***
Sensitivity7 * ** ***
Productivity8 * ** ***

1. Higher voltage provides better precision and accuracy for elements such as Pd, Rh, and rare earth elements
2. Silicon drift detector (SDD) technology allows the collection of higher count rates and thus improves precision, sensitivity, and enables light element detection vs. Siliconpositive-intrinsic-negative (Si-PIN) technology.
3. More beam conditions with different filters optimize measuring conditions, meaning better precision and sensitivity for analytical lines with different energies.
4. The limits of detection are given for cordierite and depend on the testing time, the interferences/matrix, and the level of statistical confidence
5. Indicates the degree of closeness to the true value
6. Indicates how repeatable and reproducible measurements are.
7. Indicates the ability to detect small amounts of PGMs.
8. Economic productivity: sample throughput and economic recovery of Pt, Pd and Rh.

Conversely, converters with a metallic substrate are separated using magnets and winnowing from the wash coat powder containing precious metals after being shredded or milled.

Materials are pulverized to a maximum 250 µm and loaded in XRF sample cups or sample bags for analysis.

Materials are pulverized to a maximum 250 μm and loaded in XRF sample cups or sample bags for analysis. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

The PGM content of wash coats from metallic catalytical converters is generally much higher than for converters made of ceramics because of this enrichment. 

For both types of converters, the materials are pulverized to usually less than 250 μm particle size, loaded in XRF cups and placed in a test stand for analysis.

Results

Table 1 shows the results for the analysis of 3 commercially available reference materials. The values of Rh, Pd and Pt as measured with a Niton XL3t 951 GOLDD+ analyzer are in strong agreement with the certified values.

Table 1. Typical results of analysis for commercially available automotive catalyst certified reference materials. Source: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

Materials/Elements Niton value (ppm) Certified value (ppm)
NIST SRM 2557
Pt 1110 ± 20 (2 σ) 1131 ± 11
Pd 230 ± 10 (2 σ) 233.2 ± 1.9
Rh 130 ± 10 (2 σ) 135.1 ± 1.9
NIST SRM 2556
Pt 690 ± 30 (2 σ) 697.4 ± 2.3
Pd 310 ± 10 (2 σ) 326 ± 1.6
Rh 40 ± 10 (2 σ) 51.2 ± 0.5
BAM ERM-504
Pt 1720 ± 60 (2 σ) 1777 ± 15
Pd 290 ± 10 (2 σ) 279 ± 6
Rh 330 ± 20 (2 σ) 338 ± 4

 

The correlation curves between lab results (fire assay+ICP) and concentrations measured with the Niton XL3t 951 GOLDD+ are shown in figures 2 to 4.

Correlation curve for Pt.

Figure 2. Correlation curve for Pt. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

Correlation curve for Pd.

Figure 3. Correlation curve for Pd. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

Correlation curve for Rh.

Figure 4. Correlation curve for Rh. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

There is an excellent linear correlation over a wide range of concentration between lab and measured values for all the elements determined in 130 samples; the coefficients of determination R2 and the slopes are both close to 1. 

For the tested elements, the average relative difference between measured and laboratory values was 3.8% for Ph, 2.8% for Rd and 4.4% for Pt. 

Examination of these results shows how robust the analysis is compared to considerable matrix changes and sometimes very high concentrations found in the 130 samples for relevant concomitant elements like chromium, iron, zirconium, lanthanum and cerium.

Proficiency Test

The well-established XRF company Fluxana3 organized a proficiency test for the analysis of two samples, FLX- CRM 132 and FLX CRM 133, under lab code #9 and Thermo Fisher participated. Table 2 shows the results.

Table 2. Results of the proficiency test. Source: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection

  Mean Niton XL3t 980 Value ± sd (ppm) Certified Value ± uncertainty (ppm)
FLX-CRM 132
Pt 1668±18 1673±27
Pd 1758±16 1770±73
Rh 284±6 295±12
FLX-CRM 133
Pt 1062±10 1075±40
Pd 460±4 465±28
Rh 232±4 242±18

 

Additionally, the report issued by Fluxana4 once again demonstrated excellent accuracy of analysis when using the Niton XL3t 980 (same basic instrument as XL3t 951/981).

Conclusion

Niton handheld XRF analyzers accurately analyze ceramic catalytic converters from diesel or gasoline engines as well as wash coats from metallic converters and blends of those materials. 

Whether it be for people or companies recycling or trading spent automotive catalytic converters, Niton XRF analyzers are the ideal tool to provide a dependable analysis. 

The main benefits of using Nitron analyzers are: 

  • Low cost of ownership and fast return of investment
  • Easy to use as compared to lab analysis that requires specialized knowledge
  • Real-time analysis
  • Proven accuracy over many years of use 

References 

  1. Johnson Matthey, Pgm market report February 2021 http://www.platinum.matthey.com/
  2. http://www.platinum.matthey.com/
  3. https://fluxana.com/products/reference-materials/proficiency-tests
  4. https://fluxana.com/images/products/Ringversuch/FINAL_Report_RV_2017_01.pdf 

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Handheld Elemental & Radiation Detection.

For more information on this source, please visit Thermo Fisher Scientific – Handheld Elemental & Radiation Detection.

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