Grantee Research Project Results

Final Report: PanCeria: Catalytic NO and CO Emission Control Unit for Small Off-road Engines

EPA Grant Number: SV839488
Title: PanCeria: Catalytic NO and CO Emission Control Unit for Small Off-road Engines
Investigators: Crocker, David A. , Tam, Kawai , Rupiper, Amanda , Abdul-Aziz, Leslie , Gracia, Kyah , Ramirez, Ariel , Williams, John , Elliott, Charles , Lau, Michelle , Trujillo, Marisol Reveles , Beltran, Sergio Gomez
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Phase: II
Project Period: May 1, 2019 through April 11, 2020 (Extended to October 31, 2023)
Project Amount: $74,926
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2019) Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Air Quality

Objective:

Air quality has deteriorated steadily since the turn on the twentieth century, primarily due to substantial NOx concentrations – leading to the formation of smog. Smog has become a serious factor in human health as it promotes respiratory complications and diseases, heart problems, irritation of the eyes and nose, weakened immune systems, and shortened life expectancy, leading to substantial number of hospitalizations and in extreme cases, deaths [1]. Domestic governments – Federal, state, and municipal – and international governments have passed legislation aimed at reducing smog and its adverse health effects [2]. However, these regulations often focus on automotive, manufacturing, and energy industries. An area that is often overlooked is the contribution from small off-road engines (SOREs), equipment with a spark-ignition engine that is less than 25 horsepower, which include lawn and garden equipment (LGEs), generators, specialty vehicles, and logging equipment.

PanCeria’s main objective is to develop a catalytic converter capable of reducing nitrogen oxide (NO), carbon monoxide (CO) and particulate matter (PM) from SOREs used in lawn and garden maintenance equipment, such as lawn mowers, leaf blowers, and generators. These efforts concentrate on benefiting human health and overall human welfare.  Although the impacts of such a device go beyond human health, by improving the air quality PanCeria is making positive efforts to improve the longevity and continuous improvements to the planet, to people and to prosperity of all life.   
The design for PanCeria has the goal of achieving a reduction of emissions through a two-stage setup including a mesh wool filter to remove particulate matter while a copper-cerium oxide (Cu/CeO2) catalyst is utilized for the reduction of NOx and CO. The catalyst is designed to lower engine emissions of nitrogen oxides through an oxidation pathway involving the reduction of NO by way of CO oxidation, carried out through the following reaction: 2NO + 2CO + O2 → N2 + 2CO2 [4]. This oxidation is accomplished as engine exhaust is passed through the device and the exhaust stream flows over the Cu/CeO2 catalyst. This reduction must be carried out at high temperatures as required by the catalyst, which becomes activated only at high enough temperatures between 200 and 350 degrees Celsius [4]. PanCeria will offer a compact and cost-effective device geared towards keeping existing small engine machinery in compliance with air quality regulations. These efforts will facilitate environmental justice for sustainable communities to reduce the impact of air pollutants on people, the planet, and human prosperity.

Summary/Accomplishments (Outputs/Outcomes):

The 2022-2023 team focused on using the previously designed catalyst to develop a prototype design that would be tested on various SORE equipment such as a gasoline-powered generator, lawn mower, and leaf blower. Due to time limitations, rigorous testing was conducted on the lawn mower only which was the piece of equipment that was determined to emit the highest concentrations of pollutants compared to the others. All emissions and exhaust experiments were conducted at the Center for Environmental Research and Technology (CE-CERT), part of the Bourns College of Engineering at the University of California, Riverside. Prior to testing, it was discovered that an incorrect calculation may have been used by the previous teams to obtain the 5% weight loading so new catalysts were synthesized by the 2022-2023 team resulting in catalyst weight loadings ranging from approximately 1 to 10%. The new catalysts were applied to the monolith housings using the previously utilized dip coating method and were subsequently tested in the experimental design developed to fit onto the exhaust port of the SORE equipment which is described below. 

Figure 1. (left) Block flow diagram of experimental System; (right) Catalyst chamber and monolith support

The block flow diagram illustrated in Figure 1 shows the entire system including the testing equipment. The source stream is the direct exhaust coming out of the lawnmowers exhaust port which is then piped into the catalyst chamber illustrated in the top rightmost diagram in Figure 1. The hot exhaust then flows through the cordierite puck coated with the catalyst which reacts with the exhaust. This treated air then flows further down the chamber and out towards the back. A sample of the exiting gases were collected via copper tubing which acted as a heat exchanger to rapidly cool the gases to a safer level for the Horiba PG-350 gas analyzer. The copper tubing leads the sample into the gas analyzer where the compositions are recorded. The treated exhaust gases that were not collected by the copper tubing were allowed to vent to the atmosphere.  

The tested catalyst-loaded pucks ranged in % weight loadings of Cu:CeO2 from 1.1% up to 5.6%, with sample data displayed below for the PC dip M2 catalyst which had a loading of approximately 1.3% and was created utilizing the wet impregnation method. The lawn mower used for the experiment ran for approximately 30 minutes to reach steady-state operating conditions prior to taking measurements. This was to allow for minimal fluctuation of the raw untreated engine emissions when recording the NOx and CO levels from the Horiba PG-350 gas analyzer shown in Figure 2 below as Raw Run avg,  respectively. 

Figure 2. Graphs A and B above display sample data for the NOx and CO emissions obtained in each run (1-4) compared to the average untreated emissions (green bar) from one two-hour run. Runs 2 and 3 show a relative decrease in NOx emissions throughout the 100 minutes compared to runs 1 and 4 where the treatment was for 30 minutes. 

Table 1 shown below displays the averages for the untreated steady-state emission streams from the lawn mower along with the hourly averages from the treated emissions and their respective reduction percentages for the total length of treatment using the PC dip M2 catalyst 
(1.3% Cu:CeO2 loading). 

Raw Source Emissions		Catalyst
Species	30-minAvg. (ppm)	PC dip M2 (PanCeria dip-coated) --- 1.3% Cu: CeO2 loading
NOx	80.24
CO	6304.64

Run Time (hour)	Avg. NOx Concentration (ppm)	NOx Reduction (%)	Avg. CO Concentration (ppm)	CO Reduction (%)
1	37.44	53.35	2908.78	53.86
2	25.50	68.22	1436.74	77.21
3	22.25	72.27	1285.76	79.61
4	27.12	66.20	1128.31	82.10
5	27.14	66.18	1311.22	79.20
6	69.04	13.96	6027.94	4.39

 

Table 1. Sample data for the untreated and treated NOx and CO emissions from the lawn mower; untreated data displayed for 30-minute (steady-state) average of emissions, and the treated data displayed hourly over a 6-hour run time.

Estimated Device Cost: For the finished device, the estimated cost for the prototype without the housing will cost approximately $63 USD per unit (table 2 above). This value is only an approximation as the current phase of the project only involves testing the feasibility of the catalyst that will be used in the device. The current apparatus design will be improved upon, focusing on the development with the end user in mind in the final stages of the project. 

The experimental data provided above pertains to testing that was conducted using a catalyst-loaded puck with an approximate weight loading of 1.3% Cu:CeO2; this data was chosen as the example to help demonstrate the proof of concept for the PanCeria prototype. One of the goals for the PanCeria project was to determine the most optimized weight loading of copper to cerium oxide that would demonstrate a high reduction of NOx and CO emissions while minimizing the amount of material consumed during production of the catalyst. The data displayed below shows the team’s attempt to achieve emission reductions from synthesized pucks that were tested with differing % weight loadings, ranging from 1.1% up to 5.6%. Along with the varying weight loadings, these catalysts also differed in their respective method of synthesis, with runs labeled NPC 5,7, and 11 utilizing the wet impregnation method while catalyst runs labeled Soni 5, 6, and 7 involved the method of sonication to create the catalytic material (the former were created by the 2022-2023 team while the latter were synthesized by the 2021-2022 team). These tests produced varied and ultimately inconclusive results that did not allow for the determination of emission reduction as related to Cu:CeO2 weight loading and synthesis method. Sample results for these one-hour tests are displayed below in Figure 3. 

After examining the reductions from various copper weight loadings, we saw a 70% reduction in NOx for the catalyst with a loading of 1.3%, some reduction in the CO concentration in the 1.7% puck, and an increase in NOx emissions for the puck coated with a 5.3% weight loading. The increase of emissions in the 5.3% puck may be due to unreacted NOx in the catalyst synthesis step. The unreacted NOx could have required a longer heating period due to an increase in the copper nitrate to reach a 5.3% copper loading. The team hypothesized that there were unreacted NOx remaining after synthesis because the puck had about 3 times the amount of copper nitrate and not enough nitrate was removed in the calcining step. Therefore, when the catalyst puck was used in the run, the unreacted NOx was released and caused the readings of NOx to be approximately 90 ppm, compared to the untreated baseline concentration of about 60 ppm. From these results, it was determined that the procedure for catalyst synthesis should be given even more attention to find the most optimized method of achieving the desired weight loading for each catalyst. While the greatest reductions were observed from tests involving puck-loadings near the low end of the examined range, the team still predicts that with a properly optimized and standardized synthesis procedure, still higher emission reductions may be reached with higher Cu:CeO2 ratios. 

Conclusions:

A proof of concept has been demonstrated for the reduction of NO by CO oxidation over a Cu/CeO2 catalyst. The tested catalysts were capable of showing a reduction of up to 70% with a puck of a copper-to-cerium oxide loading as low as 1.3%. Future teams should explore the maximum copper loading that could be achieved in the synthesis as well as the positioning of the puck in the catalyst chamber. Maintenance on the lawn mower used for the experiments should be continued by future groups with the possibility of also testing poorly maintained engines to see the lifetime and reduction achieved by the catalyst on engines of varying quality. Further testing could also continue exploring California's change in the fuel compositions throughout the year to see how the catalyst handles and how its selectivity may change. 

References:

[1]    EPA. Environmental Protection Agency. Smog - Who Does it Hurt?
[2]    EPA, “Smog, Soot, and Other Air Pollution from Transportation”
[3]    Board, California Air Resources. "Small Off-Road Engines (SORE)." Small Off-Road Engines (SORE). N.p., n.d.
[4]    Snytnikov, P.V., Stadnichenko, A.I., Semin, G.L. (2007). et al. Copper-cerium oxide catalysts for the selective oxidation of carbon monoxide in hydrogen-containing mixtures: I. Catalytic activity. Kinet Catal 48, 439–447. https://doi.org/10.1134/S0023158407030135

[6] Moreno-Castilla, C., & Pérez-Cadenas, A. F. (2010). Carbon-Based Honeycomb Monoliths for Environmental Gas-Phase Applications. Materials, 3(2), 1203–1227.
https://doi.org/10.3390/ma3021203

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this project

Progress and Final Reports:

Original Abstract

2019 Progress Report

2020 Progress Report

2021 Progress Report

2022 Progress Report

P3 Phase I:

PanCeria NOx Reducing Device: Selective Catalytic Reduction System for Emission Control of Small Off-Road Engines  | Final Report