Yes - absolutely.  Smaller particles are aggregated but expose much of the surface area for BET. See:

Nov 11th, 2008. Dispersion and nanotechnology  http://tinyurl.com/hpywsge  and

'Micron sized nano-materials' Powder Technology 174(1):6-9 · May 2007

It is possible, especially if the experiments were done with N2. Did you check the total pore volume?

The particle size has little to do with the surface area since both happen on completely different scales. Surface areas of hundreds of m2/g are typically associated with pores in the lower nanometer range (micropores, maybe lower meso-pores following IUPAC classification). Particle sizes are on the order of micrometers and higher, so there is a difference of at least 3 orders of magnitude. I would also imagine that N2 would not provide surface areas as high as 1000 m2/g due to the limited accessibility bof N2 to pores that are small enough to make up such high surface area. CO2 can access pores down to few Angstrom and this is where the surface area sits (such as in zeolites).

Hope this helps

Thank you all for your helpful support, By the way you could have a look on below results and help me to understand it. 

Structural parameters of MCM-41 and Ionic liquid grafted on MCM-41(MCM-41-M-V)

The following are data from BET  with N2

Samples      BET Surf Area  Pore Volume     Pore size         Particle size

MCM-41                     1020                 0.974            3.817nm                 5.880 nm

MCM-41-M-V               484                  0.329            2.714 nm              12.372  nm

Data from Laser particle size analizer

                                                           Samples                      Average particle size

                                                             MCM-41                                17 Micrometer

                                                             MCM-41-M-V                        2.6 Micrometer

1. My expectation  from Laser particle size analizer was to see  MCM-41 with lower average particle size compare to MCM-41-M-t as it in in BET data.

2.Could some one help me to know why data of particle size from BET with N2 are total different from average particle size data from Particle size analyzer? 

What are your units of size?  Microns in both cases?  What is the density of the sample?  How have you dispersed your sample for the laser diffraction experiment?  Have you followed the BDAS route?  See (registration required):

PST & BDAS - An acronym approach to laser diffraction method development

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190815PST

Trying to check you're comparing like with like.

For BET unit  nanometer and the density of  sample is around 2.3 g/cm3

Thank you  for your generosity,  

@Francois  Before I begin a reply, let me ask you one question for you to research. 

What is the diameter of a hydrogen atom?

Then take a look at what you've posted above.

Note that BET does not measure particle size.  BTW, neither does laser light scattering.

For information about Diameter of Hydrogen atom you could have a look on last link.

About  measurement  of Particle size by BET data is total possible. Attached links and paper can confirm it.

http://jcpr.kbs-lab.co.kr/file/JCPR_vol.14_2013/JCPR14-2/JCPR14_31.pdf

https://www.researchgate.net/post/Particle_size_calculation_based_on_BET_data3

http://www.micromeritics.com/Repository/Files/A_Case_study_in_Sizing_Nano_Particles.pdf

https://en.wikipedia.org/wiki/Hydrogen_atom

@Francois Is it normal when someone asks you a question to provide a Google link and say “you could have a look on last link”?  Did you actually read through the link you provided? You may want to consider a career outside science if you cannot critically evaluate literature and attempt some understanding of the basic principles.  OK, why did I ask you about the diameter of the hydrogen atom?  In your provided link, the diameter is stated to be 1.1 Ångstroms (‘about twice the Bohr model radius’; we’ll not get too detailed here on why this ‘size’ is variable) so this is 0.11 nm.  In your earlier post you quote the pore diameter and particle size (more on this later) for MCM-41 as 3.817 and 5.880 nm. The quoting of 3 decimal places implies that you (or the technique) can split the hydrogen atom by a factor of about 100…. Your earliest science lesson (at aged 15?) should have taught you about numbers of significant digits.  Quoting ridiculous numbers of decimal places does not imply accuracy – rather it indicates an inability to understand what you’re doing and the precision with which any number can or should be stated (at best 3.8 nm preferably 4 nm for the MCM-41 example above).  On to your other points in a separate response below.

You state: “About measurement of Particle size by BET data is total possible”.  I stated earlier that BET does not measure particle size.  Do you know what BET actually measures or what can be derived (with assumptions) about particle size?  What is the difference between measured and derived parameters? This is fundamental to understanding the science behind your measurements (assuming these have been correctly carried out).  BET measures the amount of gas (often N2 at its boiling point: - 196 C) absorbed onto a surface.  With assumptions about the particle shape and form plus absorption stoichiometry, one can deduce a pseudo-particle size (SSA = 6/D[3,2] where the D[3,2] is the Sauter Mean diameter).  Actually READ and understand the link you provided in: https://www.researchgate.net/post/P...size_calculation_based_on_BET_data3

I also stated that light scattering does not measure particle size.  Why did I say that?  Light scattering measures the light scattered from a group of particles and equates this to a particle size distribution of equivalent scatterers (usually spherical). So, consider a sponge. This will have 'high' gas absorption which means deduced 'small' particle size.  With light scattering the majority of scattering arises from the edge of the particle – that is the edge of the sponge.  This will be much larger that the equivalent diameter deduced from BET where the gas molecule can penetrate all the pores of the solid (micro, meso, macro etc) .  So, the size numbers will be different depending on the porosity of the material and the extent of aggregation or agglomeration. . Neither BET or light scattering measures size directly.  That’s why you need electron microscopy to understand something about the basic morphology of the solid. You as an aspiring scientist must try to understand why 2 different answers can be both correct in particle size analysis.  This tells you some fundamental things about the nature of your material. This is my last posting in this ‘discussion’.

Thank you very much Alan F Rawle, the  above information is  clear and enough and I still have many thinks to learn from scientists like you that is why I am here at researchgate.net

According my view, particle size is decreased and automatically surface area/ volume is increased , that means mass is increased.

Thank you very much Prof Alan F Rawle.